Of course yes, I agree. In the same instance however, its a different skill set entirely, but this is how it varies. A composer can play instruments, write scores and orchestrate. Ok fair. A producer of Skrillex's calibre can also compose, can play instruments, write scores an orchestrates. However, in Skrillex's case, he can also engineer, which is something that 90% of people can't do. Its a skill that is learnt by training your ear, knowing when cetain things do. I've spent the best part of 10 years developing my engineering skills and its only now that I believe I'm ready to take on the big boys. A composer couldn't do this. He is trained in a different way, this is why they always have an engineer at hand.
I visited Air Studios near Camden, during the recording of the first Pirates of The Caribbean. Everybody was doing there thing, but this poor guy had to listen to every single instrument of the 200+ man orchestra and piece together the puzzle. Without him, it would sound like a mess. And when I say piece together - each instrument is rigged with a mic, so each single instrument has to be engineered.
So yes, I see what you say, but what we do, they wouldn't have a rats in hell chance. Also, there is a difference between an engineer and a producer. 99% of producers cant engineer. The likes of Skrillex and myself, can lend our ears to both and I'm proud with what I've achieved.. I've just got to make serious money from it now Lol