Guitar is an awesome instrument, and that is why it's mainstream. Is it overdone? My guess would be yes. But there's a reason that it's overdone. It's overdone because people like it. Perhaps music is getting stagnang; I don't think so. If guitar was the only instrument that was used, then I would agree. But through the use of other instruments, such as horns, piano, drums, cymbals, orchestras, synthesizers etc., the music stays interesting. And there is a lot that can be done with a guitar, and there are many different kind of guitars.
In the past, certain instruments still 'dominated'. Classical music used a lot of the same instruments (Example: piano) in most of the pieces. It's because the instrument fits well with the sound that is trying to be created.
There is music available today that does not feature the guitar at all, or as extensively. Take classical music, and jazz, for example (and yes, there is new classical). And there are bands that use additional instruments to make their music more complex - for example, Rhapsody. there are options out there if you want to listen to music without guitar. The thing is, most people want the guitar in their music. That is why it is popular. It's the masses that make the decision, and the masses like guitar. If guitar were truly 'overused', people would stop listening to it, and it woudl no long be popular.
