The Trust Characters take too long to do their attacks.

[EdwinLi]

That only applies when you're actually using them to run the dungeon for the story. Beyond the story, you have to level them up just to see them in the later dungeons. So if their intent was as you say, then their level reset after you complete the story runs counter to that design.

Well, I have said before in other posts, they may have plans for Trust system beyond what we have now that will involve the Leveling aspect of Trust but since we have the Bare Bone version right now the only thing we can do is just level them to unlock the Title, Achievement, and 1st set of Alternate Outfits.

The MSQ version in 5.0 can be considered the Trial version of Trust System and we unlock the actual Trust System once we complete 5.0.

As of now I just treat Trust System as a alternative to leveling through dungeons in a more solo player experience for the MSQ Dungeons. They also doubled the exp in 5.05 update so players can easily max level the characters with only 1 job with average run pero level for trust being 3 runs per level (2 if enough exp carries over.)