Bono is incredibly soulful and has a great range to his voice, he can sing low, high with grit, without grit, with attitude, without attitude.... Bono officially has a higher vocal range than Mercury if you look for the facts you will find it.
Not saying Freddie is bad by any stretch, he was a great front man and a great rock singer. But I find his vocal performances all too samey for my liking. There is not enough variety with Mercury to make him superior to Bono,
U2 are a greater band for quite a few reasons, their longevity is a major factor.