Bah! After a few levels Ataraxia isn't really needed.
I find that, on my levels, TP is in plentiful supply for the most part. At around 47-52 Rune has all his special abilities to use as well, leaving a ton of TP for him. Chaz normally tuns out fast if you use Megid a lot though, but by then his special skills will last the fight without any trouble. And Rika usually runs out of TP fast if you get spammed with Megid by PD and keep using Nasar, unless you have a ton of Star Dew.
Ummm what were we talking about? Oh yeah! Why Kyra and Hahn are better choices than Raja. Well not really I guess. Hahn and Kyra are great for adding extra punch to your party. But then Raja has Ataraxia, Miracle and Regen. I'd say you should take him if you're on a lower elvel anyway. You'll need his skills then.
Oh and the slashers are awesome too, both in the Garuberk Tower and on the surface of Dezoris.