Among them was an extensive scene where Kirk is briefed by Admiral Nogura, where it is specified that the fleet is close to Earth but is just slightly too far away to arrive in time (V'ger is going to get to them in 8.6 days, but the nearest other heavy cruiser is nine days away). There IS also one other ship close enough to intercept V'Ger, the USS Aswan, but Kirk says she's a "light cruiser" with "less than half" the weapons and defence systems of the Klingons that V'Ger has already licked. The Enterprise is the only ship available with the technology to maybe take on the intruder, which is why she gets pressed into service (and Kirk, against his better judgement in this draft, accepts command of her and rushes to try and pull together a crew with enough experience to take out as quickly as possible).
Hindsight is 20/20, but I'd much rather have watched this scene than the endless shots of V'Ger's interior and crew reactions. It could easily have been re-written to depict Kirk's arguing that he'd be a better choice for commanding the mission than Decker.
To be fair TMP does tend to condense the same information into a few scenes, but it does it in much broader strokes than the earlier drafts. As such we get completely the wrong impression from Kirk's line about Enterprise being the only ship in range. The Phase II version cleverly addressed this plot point, while still keeping the fleet far enough away that it was the Enterprise which was being forced to respond.
Of course there are other changes made during the rewrites that were for the better. IMO making Decker the presumptive-Enterprise Captain was excellent change because it opened up the possibilities of more conflict between him and Kirk and made him a more fully fleshed-out character. IIRC in the Phase II draft he's not even an Enterprise crewmember but is actually an Executive Officer on Earth awaiting assignment to his first command elsewhere (the USS Boston), who Kirk shanghais into becoming the Enterprise XO due to him happening to be both qualified and available. The final version, eliminating the Boston and just making Decker the Enterprise captain-in-waiting, is much cleaner.
(I like the way the Phase II version gives us just a little insight into exactly what Kirk's job is
in the Admiralty. His duties seem to involve the actual planning behind the deployment of officers, and he's instinctively able to tell Nogura which officers are assigned to which ships when asked. It's a nice little glimpse into the proceedural aspects of Starfleet Command which were likewise lost in the subsequent rewrites.)