Even if I was fighting an untrained fighter, I'd prefer he be a skinny dude rather than a bodybuilder or some other sort of big, strong guy.
I remember freshman year in college there was this guy on our floor who had been lifting weights for a few years and was bigger (bulkier) than everyone else.
Another guy on our floor did kung fu and had a rebreakable board. One day we were messing around holding the board for each other and breaking it and stuff, and the weight lifter dude said he wanted to try.
My friend held it while the weight lifter punched it. He broke it ok, but with really strange form, like he had never punched before and was just trying to muscle his way through it.
Like I said, it got the job done, and I'm sure it would hurt to be hit by that punch. But he obviously wasn't trained and probably wouldn't have done too well in a boxing fight.
Train that guy to throw a punch and to fight and he'll be a formidable, strong fighter.
Coordinated strong people are scary.
Bodybuilders often seem to suck at new things for a couple reason:
1) people naturally assume they will be awesome, so they get a little more flack for sucking than a skinny person would
2) as a result of their bodybuilding training, they are good at specific things (the muscular endurance and time under tension required for hypertrophy). Many of them don't have much cardio ability and tire easily. Cardio burns calories and is counterproductive to their goals sometimes. This is much like a marathoner who cannot squat a lot; because of his training, he is very good at one thing: running distances. Ask him to do 6 sets of curls with 75% of his 1RM and he might not be able to finish it.
3) some of them who do
only weight lifting and have no other sport experience can be awkward when they first start playing a sport due to lack of body awareness. See #1.
4) a tendency to muscle through stuff, because usually they can. In grappling class, the noobs would always tire after a few minutes of grappling because they're trying to use strength the entire time. The more advanced people just wait it out. Of course, once they learn
when to use their strength, it becomes a huge advantage
Man, back when I was like 18 I used to talk crap about weight lifting and bodybuilders. I really did think they were slow, inflexible, and basically every other TMA myth there is. It's like "pssh, I'd hit that guy 3 times before he even finished his first punch." And my favorite "I don't wanna get too big" (as if it's so easy to just accidentally bulk up and wake up looking like Arnold)
Good thing I never got in a fight. I would've gotten destroyed