There's a reason I was shocked that Rita is actually very practical to control in battle. Her spells come off fast enough, and they're easy to work with. Furthermore, the existence of Overlimit = Instant Spell Casting adds another thing to her.
I will not defend controlling Mages in any other Tales game, outside of MAYBE Sheena in Narikiri Dungeon 3, but that doesn't count.
And...Genis felt like the obvious LVP of ToS, barring maybe AI Controlled Sheena (I'm told PC controlled, she's a beast at tying up enemies.) His spells are weak, they take too long to come off, and the damage is unimpressive until late game. Furthermore, enemies are good at getting around them. I think most will agree he's the worst Pure Attack Tales Mage in the series for a reason.
So no, Elfboy, that's not "Early game Genis." That's just "Genis in general" <_<. It doesn't help that what Genis would be good for (Tying up enemies), Zelos/Kratos can technically pull off as well, getting a lot of higher end spells too. They miss out on the really strong ones like Meteor Swarm, but still get big AoE moves, even if the spells don't hit very hard. No, I'm not suggesting you use them as Mages, just saying that when it comes down to it, they aren't that much worse than Genis at it, which speaks heavily for Genis' worth. To add insult to injury, Kratos/Zelos also have some healing which can be helpful in a pinch. Difference is, Raine's healing is a lot better so they can't totally replace her, more just work in a pinch if she's busy casting something else like Resurrection. Genis is totally one dimensional, and not good at that lone dimension.
He's a lot better in ToS2, where he hits like a truck. Seeing Meteor Swarm do like 3000 damage (ToS2 has a generally lower damage curve than other Tales games) to enemies...sometimes multiple times...is pretty frightening, and he hits much wider areas than ToS1, as well as casting spells a little faster too.
Jade is the first Tales Mage, in any event, who was good for the RAW POWER thing...and I think he might be the only one. Well, Rita's spells hit hard, but outside of her really late game stuff, I don't remember them being especially painful unless she's hitting a weakness, more just "A little better than fighters." What made Rita stand out was her general utility of said damage; its ranged, hits areas, gets around enemy blocking, what have you. The fact that she can be controlled and not feel like a burden was just icing.
Actually, ToV is pretty awesome on playable options. Yuri, Repede, Rita and Judith (...if kept to simple stuff, unless you're CRAZY and actually learn her complex nonsense) are all very workable and play differently. Never bothered much with Karol mostly cause I hate tank style playing in ARPGs, but wouldn't shock me if he was practical. This leaves Estelle, whose a healer (so you probably want her AI controlled anyway), and Raven whose...got too many options that playing as him would limit without severe armounts of micromanaging (THANK GOD Tales games let you changes skills mid battle), to the point where its just easier going "Fuck it, let the AI control him."
Pity Flynn is only a temp, as he'd be another interesting PC to work with (though, he might be too similar to Yuri?)