Dynamics anyone?
I've known several folks with the fast is better thing (including me 20 years ago). The thing is it's not really impressive and wont make a statement if you do ANYTHING all of the time. Whether its funky slap bass grooves, or two handed tapping and whammy bar tricks, it doesn't matter. What if you're going fast all of the time, and then one day you decide we need a fast tune. What then? You're already maxed out. Going from 200bpm to 250bpm has zero impact. Going from 75 bpm to 250bpm is a slap in the face and a punch in the gut all at the same time.
This same theory applies to volume as well, and most if not all guitarists go through this too. "I have to be loud to get my sound". Ok there is some truth to that, but it is heavily outweighed by the B.S. You only be loud enough to be heard with acoustic drums. Notice I said "with" not "over". The loudest thing should be the vocals regardless of genre, because that's what people relate to.
The question you have to ask is; is it a band or is it "WATCH ME DO THIS KILLER RIFF!"? If you friend the guitarist is just wanting to show off, a big mirror and some colored lightbulbs should be enough to make him happy. However, if he is interested in being in a band, he needs to grow up a bit as a musician.
BTW - I grew up listening to metal and Yngwie Malmstein was my god back in '84, but I have grown up a bit. I still listen to metal, and Yngwie, but there is more to life and a good show.