Squadrons were smarter than Trusts as they actually had abilities they could use and reacted differently to trash mobs and bosses, using AoE when relevant. Trusts may have an AoE in their loop of attacks they do, but mostly just single target everything down slowly.

As for content cut after the release of ARR, it's mostly just some steps from the slog that is the MSQ from 2.1 to 2.55 that involved you just running from one NPC to another.
Not so much cut, but things have been practically abandoned. Like Guildhests, which were (and still are) kind of like an extra tutorial... The hunting log for some extra XP... Chocobo companion, who is so abandoned that the chocobo skill trees have Accuracy as a stat, which stopped being a thing at Stormblood's release... And during ARR they experimented with WHM and BLM having shields, but I think Leviathan EX was the last thing to have those.