Well, the difference is that Cless is still able to deal damage quite nicely even when his TP has run out, whereas the spellcasters are much more dependent on TP in order to be useful.
So I was almost expecting constant problems with keeping their TP up in dungeons etc.
But then again, I guess the fact that you always gain back some TP at the end of the battles is an important advantage, and then there is of course that ever-useful Fairy Ring accessory which cuts all TP consumption by half.
It was still a somewhat unusual party though, normally a party of four characters will include at least two fighters, and rarely as much as three spellcasters.
This does happen at one point in FF9 during the Iifa Tree part though, but not for that long.