Auron's slow, yeah, but there are remedies to that: like Haste, and Slow. Sending him off down Tidus' sphere grid path after he's maxed his own one out also balances the speed off.
My version is wearing a bracer with the auto-haste, auto-phoenix, break HP limit and auto-regen properties, for example. My versions of Yuna and Tidus basically have the same things, except that theirs both have "Ribbon" instead of auto-regen. They all have their ultimate weapons (fully unlocked) and even Yuna does straight 9's when she hits something with a basic attack, unless it has a stupidly high defence. Tidus and Auron do straight 9's to anything.
My problem with Kimahri is that's he doesn't really provide a fixed role - he's a jack-of-all-trades, master of none, whose development is determined by what you want to do with him - and though he may be faster than Auron, he doesn't hit as hard, neither is he as quick as Tidus or Wakka. Similarly, his magical abilities are inferior to those of Rikku, Lulu an Yuna. He's a cool enough character, and "Mighty Guard" if and when you learn it, is a really cool move, but he never functions properly at the front of the party, because anything he can do, somebody else does better.
but to each their own, I guess. I've got the three most important characters - Tidus, Yuna and Auron - so completely maxed out that it's simply not worth it to bring the other guys into play - anything those three can't handle, none of the others will, either.