Anyway, and I'm not referring to your post in particular, one should consider the basics of OS combat system before looking at other systems/games for inspiration. I'm my opinion its not a system particularly suited for buff specialists, nor one that needs a summoning specialists, considering that filling the battlefield with elementals is one of the simpler way to steamroll through the game, even at the highest difficulty setting.
I'd tend to disagree, as buffs were very, very important and quite overpowered in DOS1. I played with 2 characters only ( both lone wolves ) so having to play with 4 would be new but I reckon there COULD be a place for a buff/debuff specialist whose main job would be to empower his friends, leaving them to focus on other aspects of the game. Actually that would even make combat more dynamic and flexible ( at the expense of strategy maybe ) as you wouldn't be forced to stop whatever you were doing with your big melee juggernaut in order to re-cast his defensive buffs or whatever.
Also, Bards in Rift ( a subclass of the Rogue archetype ). They were quite fun to play, and invaluable in a group, while retaining what makes a Bard a bard : a singer and musician
