IMHO, and - spoiler alert - here comes a novel, which is spoiler-free so no worries:
The timeline holes allow plenty of headcanon by fans, where they can fill in enough of the missing pieces and enjoy both the current era and what came before. If everything is filled in, there will be even more plot holes but with the added fun of demystification that runs the risk of apathy from the audience due to added discontunity.
For example, after the Star Wars prequel "Rogue One" came out, people loved the whiz-bang pacing, but - for examples:
- Vader seems atypically far stronger than the Episode IV that immediately follows it so is he playing nice with his swordfight with the doddering old dude in the oversized Jawa cloak
- the different methods of communications and transmissions used in the prequel (2016) only adds more questions about the rather limited events in Episode IV (1997), though some can be headcanoned away
- the pacing of the whole of Episode IV could be deemed glacial by those now used to modern methods used for Rogue One, etc.
- It's not like the new audiences are going to pretend it's 1977, with lack of smartphones, email, generally more relaxed pacing and ramping it up only for key scenes, lesser amounts of incidental music, and the rest of it all as well
That'll take fans out of the drama fairly quickly. Like reading a book, where early chapter set events up, but later ones reuse the events as if they never took place, then tack on a second edition where a preface throws in previous yet arguably unneeded events to set up things, again, but in a way that (at best) doesn't mesh. SW was bad enough when Episode VI threw in another death star out of nowhere, imagine if every sequel was revolving around a death star... complete with the same frigging flaw in it!!
Assuming these new fans actually follow up with what comes after it yet made before it, if there's a chart showing any shiny new interest in Episode IV after Rogue One came out, and for how long, that'd allow a lot to infer from. Possibly. Of course, some scene tightening and throwing in a ton of new CGI will fix that because it always does. They can even add another death star into Episode V, why not.
And that's just for Star Wars. And I do rather enjoy Rogue One, the original trilogy, TLJ, etc. Even Solo had some moments making me hope for a sequel despite other moments being nonsensical, but before I digress from a topic that was tangential and thus a digression but on a contextual scale and there I go again...
...so a better example of growing too big is Doctor Who - it
never had continuity, and the modern series rather impressed in coming up with "time can be rewritten" and "fixed point in time" to nimbly get around the sheer lack of it before. Indeed, add those lines to Vickie's speech to Steven in "The Time Meddler" (since nothing between then and the modern era story that introduced the lines touched on the subject of history being changed...)
So, to get to the Trek answer for all this now that the other cases were made, which had to be because there is an overlapping main theme and points, and to cut a long story short despite having already told the long story, it's why I prefer Trek's sequels over the prequels as they're continuing on storylines for the most part and enough that expands the universe, rather than wallowing in small universe syndrome (I'll spare the tangent regarding Futurama, which already fell into that trap and I hope the shiny new season doesn't fall into it again). There's nothing much needing to be filled in, and "Yesterday's Enterprise" is an exception, but before I dovetail down that bunny hole: The Trek prequels aren't really doing much that's engaging. There's nothing that really needed answering. The Kodos episode was sufficiently set up and resolved in a single TOS episode, and did we need to see the setup dialogue expanded upon into a 2-hour extravaganza? Nope. Would a prequel fleshing that out have worked better in 1966 or 1967? Depends on how many people really dug this single episode. But TV wasn't made that way back then, it was a one-and-done. Set it up, resolve it, and next week the events won't be mentioned again and characters act the same.
Then somebody invented the 8mm home film equipment, the first equipment someone could use to record a show and rewatch it later on. But before I digress any farther:
ENT had the same problem all prequels do, and there's little that needed to be addressed. As with BSG and seeing Capricans waddling around creating the to-be future that (a) wasn't popular and (b) arguably caused more questions than the few if any it answered, but I digress again: The makers of DSC wisely moved the show into the far future so it could breathe and be its own thing, rather than living in the shadow of the original* digging up old baddies and pretending they got to "create" them in the timeline before original generation (OG) Kirk had. (if they say it's the same universe, but too much suggests they're in the Kelvin timeline, where it all makes more sense and is more readily watchable with that mindset in mind. But then, here comes a tangent, how many infinite infinite universes will come about? Life was easier when all people did was re-tell Shakespeare plays for 400 years. Imagine the cast who did it the best, put to film, and how everyone later just mimicked them. Even better, the films get destroyed so now there's this magical deified aura - like with Patrick Troughton's Doctor Who, except most of what has been recovered sorta suggests the era was more often stellar than not. But I digress.)
* Pepperidge Farm remembers when the same complaint was made by many in 1987 and 1988, about TNG clinging to TOS way
too much... and the tone and content revamp, finalized in season 3, managed to hit the cultural zeitgeist in the same way TOS had (albeit during reruns). TOS was ahead of its time, TNG found itself in time. (it's all since been history, and there has been a minor renaissance regarding season 1 in particular, at least for a number of episodes and despite the headscratchers like models of the 60s shuttlecraft in a lounge or somewhere, computer screens showing the film 1701 design wireframe for no reason since the show is ostensibly 80 years in the future, etc... if they can't sell the universe, the audience is less likely going to buy into it.)
The only real question now is, what harks back to the main subject line,
is Trek's story already fully told? I'll just say "no" as sequels can always find their own way, have their own solid feel, may or may not find the current cultural zeitgeist, be in the same universe and have some links to the past without going nuts with it all, etc. Lower Decks has managed to tell new venues, engagingly, and the use of comedy renders most of the references and callbacks less annoying than they are in the other shows running right now. I
blame thank the comedic aspects, since they seem to know when to take the stories seriously and when to add levity. But comedy is as ranged as the audience, but LD did find its own way and had a solid feel right from the start.
But YMMV.
