There's a difference between front-line capable, useful in a fight and just poor in any fight.
Mages(wizards, sorcs, etc.), not fighters, are the most powerful combat classes in the infinity engine games and NWN2, with the sole exception of very low level play, so a mage was the prime choice for a solo playthrough of BG2.
Fighters and pallies and such were always decent meatshields and even relatively good damage dealers at low levels. Clerics ruled in 3E and healing spells and buffs were always useful enough to bring even non-combat clerics along.
Poor in a fight have always been the non-dualclassed, pure thieves/rogues. I've always thought of this as poor game design, but not a deal-breaker.
When rogues nolonger suck in combat, the old excuse for rogues getting all the skillpoints and utility outside of combat nolonger holds up. The consequence of all combat proficient classes will have to be a redistribution of the available character skills.