I think heavy hitters like James or Ash always come in handy. If not for the damage output, then they can at least tank for the group. What I've always found a bit problematic is that we have one Soldier class already (James) and Garrus is an assault/sniper rifle specialist himself. In comparison, Kaidan is a one man army - not only he has both tech and biotic skills so there's no kind of defence he can't rip through, he freaking has more shields and health than my Soldier Shepard even and that's without his Barrier, and now that he can properly wield an assault rifle, his overall damage output is crazy. I've come to like giving him the Saber because, while it is a bit slower, it packs hell of a punch. Personally, I can't see myself sacrificing all this to have three Soldier-like classes instead, so I can't imagine saving Ash for more than roleplay. However, comparisons aside, I don't doubt that Ashley totally has her benefits. My main Shepard is a Soldier herself, so as far as I'm concerned, more firepower is always good.
Aw, and I don't have the Typhoon, though. Now I'm jelly.
Wait, aren't those her casual clothes in the picture? Kaidan wears armour during that cutscene. Interesting.