By the way, I have to say that I was kind of slightly offended by the title of the post. To imply that Bono can't play guitar properly or that he never learned offends me (I'll live).
I'm part of those guitarists who absolutely loathe guitar solos in general and think that they all sound roughly the same and allow guys to indulge themselves in some showing off. A dick contest, sort of. So, not being able to do a "proper" guitar solo is irrelevant, IMO.
I personally don't understand why it might offend you, but each to their own and all that!
I think it is a fairish question - he's been in a band for 40 odd years, and pretty much adds nothing musically to their live sound.
It is one of the reasons i suppose their live sound is so heavily augmented with pre recorded parts etc.
That said - there is an argument that can be made strongly for u2's sound being all about what Edge, Larry and Adam do and it's a sound loved by millions and has endured for 40 odd years.
But i do find it a little odd that he can't really add to u2's live sound musically, that he can't play and sing at same time really - it isn't about flashy solos etc.
I do wonder if one of the big reasons he does not or can't 'weave' with edge is because of how Edge plays and how Edge uses effects....maybe that makes it too difficult for Bono.
It could open up a potential new sonic avenue for them though if Bono was able to provide more musically live, but for what must be pretty good reasons they have always chosen for him maybe not to/he does not want to/can't....