Well to me, someone already said this but not having direct control over the others made me feel more like the other characters were individuals, and the main character felt more like... you.
That was probably me.
Yeah, P3's AI was a bit dumb at times, but here's the thing. Artificial stupidity can be endearing. And the fact that you don't control them and that they chatter in battle sort of addresses the "Character loses all personality as soon as they join your party" syndrome you see in a lot of JRPGs.
And besides. From a story perspective why WOULD Junpei act particularly smart in battle?
Also P3 was fairly easy as far as SMT games go. If you were ever at a point where your party members would get you killed by either doing or failing to do something, you probably weren't approaching whatever battle you were at right. The MC has like, a dozen persona's available to him. That's plenty of room to cover your bases.
Now Gambits were an awful control system. Way too much hassle to deal with and change up
Also the whole buying/finding options. It's a AI programming system. They tried to make it into more of a strictly gameplay feature than it had any right to be. It's like disallowing the player from accessing their players stats until they buy the appropriate menu command in a shop.
That and FFXII's boss battles don't have anywhere near the level of creativity FFX's had and I think the gambit system and the battle system are partly to blame. I mean, just for comparison, since I just did them, you can't really do that claw shrimp battle or Yunalesca in ATB because it'd just be unmanagable for one thing and especially with FFXII's slightly more chaotic flavor of ATB, but you couldn't do them at ALL with gambits since you're micromanaging the hell out of your turns and you just can't automate that.