The only time weight training is detremental to a fighter is when it leaves him too fatigued to train specific fighting skills and cardio properly.
There is no doubt in my mind that increased strength is helpful to a fighter, but it is not as important as cardio and fighting skills.
If a fighter can find a way to effectivly increase limit strength without compromising the rest of his training then weight training is very valuable. It is very difficult to find that balance though.
From my personal experience I have missed many training sessions because I squatted the day before and couldnt even walk up the stairs, much less fight.
I think that traditional powerlifting and body building programs are not appropriate for a fighters needs. They require more recovery time than a fighter can spare. Perhaps there is something to a bulgarian style of training for fighters.
What if you trained multiple times a day, 5 or 6 days a week, doing singles and doubles at 80% or higher, but kept the reps and sets low, and never came close to failure? I dont know personally, Ive never tried it, but it just poped into my head. Some of you guys really know your shit and id be interested in what you have to say.