ARR base wasn't a slog at all and had decent pacing.

ARR post game needed a lot of pruning, because there was no set cycle nor formula for FFXIV yet, and so they were just making stuff up and biding time as they worked on Heavensward, which they didn't even expect to be greenlit for an expansion, so you know...

Completely different circumstances. Also the setting and Ascians still had mystery then, so the Ascians could twirl their moustaches all they wanted and still be interesting, because they had intrinsically interesting questions revolving around them (Their having The Echo, Speaking The Original Language, Who is Zodiark?, How come they know true summoning?, How come they don't stay dead?)

And you could also argue the point around. While there were originally like 110 quests between 2.0 base end and 2.55 end originally (or something like that), the reason they were viewed unfavorably wasn't due to being bad or unnecessary storyline wise, but due to being too much, too many quests. Basically being in the way of new players and the road to endgame. Low investment/engagement because many many quests that were just spinning the wheels.

Dawntrail doesn't have that excuse. Dawntrail's excuse was purposely set up to be, "Well, we're having to follow a forced finale of a 10 year arc, so you gotta bear with us as we try to start up a new storyline..." This falls flat immediately to anyone with any amount of perception. Because:

1) They're calling back to Ascians and Amaurot still.

2) Endwalker didn't have to be the conclusion expansion. They could have easily gone with a Garlean buffer expansion. They weren't sure they could follow Shadowbringers' unexpected success levels, so they played to the hype train and the easiest way to make something hype is to make it the finale.

3) ARR's start came off the heels of 1.0 as a rebirth for the game, and was a new storyline using 1.0's lore. It was gripping enough to relaunch the game into a long term success. In spite of being the same sort of, "new beginning" as Dawntrail. We have to face reality here and realize that they didn't really write us a good story with good villains nor good adversity nor mystery. What's the hook? See #1.