I actually feel the opposite. I don't feel like they're bad, or even mediocre, musicians, but I feel like their solid songwriting masks a lot of their talent. Bellamy, no doubt, is a great pianist, but I felt like he hides his guitar playing behind too many effects. Unlike Tom Morello, his "guitar and an amp" style playing isn't really extraordinary, so he masks it with over the top tricks. Wolstenholme is a a stand out bassist, and Howard is an alright drummer. I really like Muse, but I feel like they're incredibly overrated.
So you think their songwriting masks their musical strengths to a degree? That sounds like they're not making the best songwriting decisions. Which kind backs up my theory haha.