Well if those are the ONLY Mindflayer abilities yeah that would suck. But if it isn't or the Mindflayer has classes then I think combat can be just as robust/complicated since it is sorta the idea that the brain-sucking would be a signature move, but only done when the best opportunity arrives.
As for stunned or feared, with current rules I prefer stunned but I would like to see some good fear roles, where you don't run away, but instead are effected differently depending on the intensity. Like look at soldiers they are obviously frightened while fighting, but they don't automatically run away, but they may get sick, aim may grow faulty, etc.