He can't play leads?
Seriously though, something I think about is that from my observation at least, in order for a band to get to be the biggest in their genere they have to be good - and have that special sauce - but they can't be too good. In other words, the more technical a player is the less mainstream appeal they'll have. Bands like Metallica, AC/DC, the Police, hell Taylor Swift etc. are in that sweet spot. bands like Dream Theater will never be any bigger because they're too technical for the average person. As for Megadeth my opinion is that while their extra technicality isn't helping them be bigger, there's something unattractive about the actual anger & resentment Dave holds in his heart that subconsciously turns people off. Regardless of the lyrical content I'm more interested in people that are fundamentally happy.