All right @G650, I'll do you one better. I'll argue in favor of what you're saying. And the reason I'm doing this is so that, instead of just going over the same points you've already repeated over and over that I already understand, you'll be able to take a step forward and see what I am trying to say.
So here's Dave Mustaine playing with the San Diego Symphony.
Now, I don't know about you, but it sounds like complete ass to me.
It sounds like complete ass because of Everything Else. He's playing among instruments with massive and subtle dynamic range, among performers who have mastered that dynamic range.
And on top of that, he's hitting notes out of tune that need to be bent into the right pitch.
I don't think anyone's going to say that Mustaine is a bad guitarist, but in this environment, his skills are underdeveloped to the point of sounding amateurish. Why? Because he always only ever played or practiced his guitar with the gain cranked to metal levels. He doesn't have a lot of mis-hits in his playing, because that's how he practiced; but dynamics, tuning, subtlety... are completely absent. Again, because this is how he practiced.
Until this concert, he never needed subtle dynamics, and being out of tune occasionally was acceptable for various reasons. But here? The guitar and symphony don't work together; it's jarring and painful to hear.