This has been bothering me for years, but I've never seen a thread that really answers the question. So, the whole Rebel Fleet shows up at the Forest Moon of Endor, drops out of hyperspace and closes in on the Death Star. The plan is for the fleet to create a "perimeter" while the fighters go in and do the dirty deed. The Rebels think they have the upper hand, but they also -- apparently -- expect the Death Star to be very well defended either way, hence the huge fleet they brought with them. They WEREN'T expecting what actually showed up to meet them there, obviously... On the other hand, once the trap is sprung and the rebel fleet is pinned between the Death Star and the Executor's fleet, Akbar tells Lando "At that close range we won't last long against those star destroyers..." The thing that bothers me is, the imperial fleet clearly outnumbers the rebels, clearly has more fighters, more troops, and a definite tonnage advantage across the board. Down on Endor you have the Ewoks as an excuse; at least they have surprise on their side. But in space, the rebel fleet is facing basically the same odds as Han Solo's little strike team, and they still manage to fight it out with the Imperials for, like, 30 minutes before the shield goes down. This doesn't make a lot of sense to me. Compare with, for example, the Battle of Scarif where the entire rebel fleet goes up against two Star Destroyers and a base and basically fight each other to a standstill until Radish pulls off the Hammerhead Slam. Compare with Athalon, where a similar-sized Imperial fleet mopped the floor with General Dodanna's flotilla. Compare Tantive-IV vs. Star Destroyer over Tatoine, and realize that the entire battle of Endor was basically that on a massive scale, since the Rebels only have CLOSE to the same number of cap ships if you include all the CR90s they brought with them. But they still manage to hold out for a considerable amount of time, at "point blank range," even with the Death Star having vaporized two of their heaviest ships. I'm clearly missing something. Do star destroyers just suck at close range? Or do they just suck in general and LOOK way more impressive than they actually are? All the specs and EU material says this should have been the mother of all curb-stomp battles and going to point blank range should have resulted in Home One being torn to ribbons in about thirty seconds flat, but by the time Lando's going for the main reactor, the Rebels are STILL holding their own against the imperials, smacking them around like... well, like EQUALS. What gives?
The Battle of Scorig lead by Adm. Raddus might have had little experiance in that type of Battle, perhaps prior to that they had engaged in more hit and run tactics rather than a full scale attack. So in the years between Scarif and Endor they got more experianced, had more experianced officers defect to them after events like the destruction of Alderran.
If the Alliance fleet had stayed where it was it would have been taken apart, piece by piece by the Death Star. By moving in on the Imperial fleet, they present the station with fewer clean shots and as Lando said, offers the possibility that a few Star Destroyers will get destroyed along with them. As for how they were relatively successful, recall that the Emperor left specific orders that the fleet remain in position and only prevent the rebels from escaping. They'd expected the rebels to either scatter or focus in the interdictors to try an punch through and escape. What they didn't expect was the Rebels going straight at them and cross their lines of fire, that left the Imperials in a less than optimal position. It also forced the fighter squadrons to split their focus from attacking the rebels to defending their own capital ships. It's still not a very tenable position for the Alliance fleet, but then this is not a carefully considered strategy, it's a desperate act meant to buy time until the ground team could come though. They couldn't keep it up for long, but this was always going to be an all or nothing engagement. If you want a glimpse at what was going on with the Imperials, I'd suggest reading this short story if you can find it.
It is possible that the fleet closing to point blank range allows it to use the bulk of some of the Star Destroyers to shield the Rebel fleet, not only from the Death Star II, but also the majority of the other Star Destroyers. Instead of staying at range and being under the guns of 30 or so Star Destroyers and a Super Star Destroyer with a Superlaser popping a star cruiser every few minutes, they close through the center and can only be targeted by say, ten Star Destroyers and the Super Star Destroyers. The other Twenty Star Destroyers would need to redeploy to get shots off at the Rebel fleet and the Superlaser risks hitting Imperial ships. This of course wouldn't save the fleet for long, but it would buy them more time. Plus this close in engagement likely resulted in the Rebels discovering a lot of the weaknesses of the Imperial ships, leading to the next year of literally hammering the Imperial star fleets across the galaxy, ending at the Battle of Jakku with the last known Super Star Destroyer in service being destroyed. Also it seems that the Rebels did complete some larger capital ships prior to the end of the war, judging by the Last of the Jedi introduction of the Republic cruiser Raddus before the treaty goes into effect following the Battle of Jakku
I get all that, it makes sense from a "stalling for time" aspect, since it certainly would have taken the imperials a lot longer than normal to press the advantage they clearly had. THAT part isn't what bothers me so much. What bothers me is what happens AFTER the shield goes down. Lando and his fighter squadrons break off and charge the death star, and Akbar apparently moves the fleet to create a perimeter as originally planned... Which is the point where they all should have died about five minutes later, and Lando should have emerged from the exploding Death Star just in time to see the tumbling debris of the rebel fleet, having been chopped to bits by the Empire. In other words, the rebel fleet goes from "backs against the ropes desperation attack!" to "Yay, we're winning!" pretty much the moment the shield generator blows. Every part of this battle gives me the impression that WITHOUT the death star's superlaser, the imperial fleet had no gaurantee of victory at all, and would actually have been evenly matched with the rebels in a straight-up fight. The superlaser was their trump card, and the shield generator on the surface was the only thing keeping that card in play.
I think/hope this would prove to be illuminating, because at this point I can't really shake the impression that the entire Imperial Star fleet was the mother of all paper tigers.
There's the deleted scene showing that the Death Star commander had standing orders to destroy the Forest Moon if the shield went down, so that covers why the Death Star didn't continue participating in the battle; it was coming about to target the moon. In the EU (and possibly in the new canon), there was also a bit about how the Emperor was using his force powers to help the Imperial personnel maintain focus in battle, and once he died, the absence of his influence cause them to become disoriented and sloppy.
First off, I think it's important to remember that these movies are fantasy adventure in the vein of Flash Gordon. It's not meant to be Horatio Hornblower in space. The keystone to the latter half of the battle was the Executor. Ackbar didn't create a perimeter, he pulled everyone in to focus on the flagship, which had itself moved in closer to protect the Death Star (an easily missed detail). They got lucky and/or the force was with them and they managed to take it out. With the ground base eliminated, the Executor obliterated and the Death Star's reactor destabilising, most commands panicked and ran. Also keep in mind that all of this would have taken a mere matter of minutes, from the shield coming down to the death of Piett. Don't underestimate the role of morale in this. Real life history is replete with superior forces routed by an inferior force, mostly because they lost their nerve. Imperial doctrine starts from the assumption that the Empire is all powerful and invincible and the rebels are an undisciplined rabble. What they witnessed was utterly unthinkable and they could barely comprehend what was happening, let alone counter it. The Empire also works on a strict top down hierarchy. With the Emperor letting his comms go to voicemail while he electrocutes him a Jedi and Piett vaporised, there was nobody left to tell the remaining Captains and Admirals what to do and no clear chain of command. It all fell apart fairly quickly. There's a little more to it, but you'll have to read the aforementioned short story for the details. I really hope that's something they never re-introduce. Aside from being an unnecessary and unimaginative solution to a problem they didn't really exist in the first place, it robs the both the Imperial fleet and the Rebels of almost all agency. It also gave us the concept of "battle meditation" which I tend to view as the beginning of Jedi/Sith power creep in the old EU. As soon as the Death Star was destroyed, the battle was essentially over and the fleet was already in disarray. The only sane course of action was to retreat and regroup because one word got out, the whole galaxy would erupt in open rebellion. They need to prepare for the next battle or loose their Empire. So far from descending into chaos, the fleet actually made the most strategically sound move possible.