How large are the expansion packs compared to ARR?

[Fynlar]

Not as large. Post 2.0 MSQ is something like 100 quests long, but post 3.0 and 4.0 up until the following xpacs is not even half that many quests (somewhere around 40-45). The number of dungeons we've gotten over time has become less and less, too.

This is surely part of their motivation for pruning ARR MSQ by 5.3 or whenever it was they said they were gonna do it.

[Sylve]

Not as large. Post 2.0 MSQ is something like 100 quests long, but post 3.0 and 4.0 up until the following xpacs is not even half that many quests (somewhere around 40-45). The number of dungeons we've gotten over time has become less and less, too.

This is surely part of their motivation for pruning ARR MSQ by 5.3 or whenever it was they said they were gonna do it.

Fewer quests to be sure, But better ones. Like, instead of a quest to talk to person A, then a Quest to go back to person B and then a third to go to person C, Its all one quest to talk to them. Stuff like that.

As far as story, All the expansions give a good 30~ or so hours, including leveling. Longer if you don't rush it.
For content … Well, Technically every expansion has the exact same amount of content in it as the previous one.
One main Raid series.
One Alliance Raid series.
One Trial/Primal series.
A set of MSQ Dungeons and Sidequest Dungeons.
One non-raid alternate content. HW had Diadem, Stormblood had Eureka. Dunno whats coming for Shadowbringers.
Beast Tribe stuff.

The stories change, but the content is the same throughout.