Speaking as someone who's programmed video game AI in the past for released AAA projects, Trusts can also be programmed to do all the above if they so choose, the only limitation is what the developers want to do.
Arguably, programming the trusts to do any complex mechanic would be easy compared to true, adaptive on the fly AI, since the trusts in this game, programming wise are effectively designed as a very simple AI: 'if x, do y'.
Like, take Dohn Mheg's intermission, where the moment the boss creates the illusion bridge, each of the trusts loads up its individual script on how to proceed and get to the other side that is unique from each other., something that could easily be replicated for any mechanic where each member of the party needs to do something different.
Trust me, their capabilities can be whatever Square wants to be, since their script for any mechanic can be as complex as needed to be. Trusts could easily do Ultimates if they were given scripts on how to perfectly complete each mechanic given buffs/debuffs and given damage buffs to compensate for the downtime while they dodge. The reason Square makes dungeon design the way it is isn't due to limitations of trusts, it's because that's their design vision for dungeons. Or laziness on wanting to have to make the more complex scripts needed for more complex mechanics.
Heck, we see more complex NPC AI inside of solo instances from time to time, showcasing the devs could make complex trusts if they so choose. it's an intentional decision that they don't, whether for design vision or for laziness.
