I think one of the biggest mechanical failings of Justice For All is related to it being the first game to allow you to present character profiles as part of an objection. It effectively doubles the amount of possible objects you can present as part of an objection. I remember there being multiple times where even when you've figured out which part of a testimony has flaws, it's very ambiguous whether you need to present a particular piece of evidence, or just present a particular character's profile. I think they were new to the idea of using character profiles within the mechanics, and didn't localize the script well enough to make it super clear whether it was expecting you to present evidence or to present a character.
I remember there was one really dumb part in Big Top Turnabout (or whatever the circus case is called) where I was trying to indicate a particular character when someone poses the rhetorical question of "Who else could've been there?" as part of their testimony, and it wouldn't accept it if I submitted the dude's profile to indicate "This guy. This guy could've been there. You know, because we already established he was in that area." But it WOULD accept it if I submitted his top hat that had been found near the crime scene.
I'm probably misremembering that scenario some, but overall I recall that circus case being frustratingly narrow in what evidence it would accept. The later games are much better about sometimes accepting 2 pieces of evidence that are more or less equivalent in relation to the current testimony. Also I believe the series eventually dropped the ability to present character profiles as objections anymore, going back to simply presenting evidence, which I think was a good move.