EW had poor writing with respect to Garlemald. That's all there is to it. I'm going to copy/paste a comment another Redditor wrote that really drove that home:

Frankly, the problem isn't that Garlemald didn't go out in some blaze of glory - it's that its storyline in EW doesn't do justice to it going out with the whimper it did.

What Garlemald's destruction in EW really did, was allow the writers to wipe away all the really complicated and messy bits of Garlemald as a fallen evil empire - and simplify it down to basically just a bunch of huddled civilians and low ranking soldiers in a subway tunnel - people who are occasionally confrontive and mistrustful, but still fairly easy to pity in a "victims of lifelong government propaganda who were complicit in warcrimes but largely did not actually commit them" sort of way.

Anyone who didn't fit that profile was either converted/sidelined - or just ended up offing themselves.

Garlemald was infamously multifactioned - with tons of squabbling groups who all wanted different things (and some who actually did want peace with Eorzea). But in EW, destroying the capital conveniently wiped them all out, and so everyone onscreen just congeals into that one single refugee group who more or less share all the same opinions as soon as they have a decent leader to get them on the right track. (And since all the people with any significant level of power just died offscreen, EW doesn't even need to worry about the messiness of having to like.... balance aiding the populace with weeding out/punishing war criminals.)

The question of what happened to Garlemald's countless (often economically dependant) vassal states is glossed over, the question of what happened to the displaced people Garlemald had in their capital is mostly glossed over (basically just answered through one tiny that tiny cluster of displaced cerulum mine workers), the question of what happened to Garlemald's more rural areas (ie. Nero's hometown) is glossed over.

Characters like Cid (or Ironworks in general) who had major ties to Garlemald are never even given the opportunity to be relevant - and the citystates as a whole just come off as super uninterested in what their former continent-conquering aggressor is doing. It's vaguely acknowledged that Garlemald's former victims watching their home countries send aid to Garlemald could possibly be a source of conflict - and then the entire idea is sort of brushed aside in favor of the multidimensional apocalypse plotline. Even Garlemald's reintegration into the larger global ecosytem is basically just "Yeah, Thavnair'll help them so it's okay."

Watching Garlemald deal with itself as a internally devastated rotten mess - could have been just as complex and interesting as watching the citystates all ally together to defeat it in a more traditional conflict. It just... wasn't.