One of the most common points made by people not liking Paul Rodgers is that he is trying to replace Freddie. To these people, it wouldn't matter who was singing actually, as they are just pissed Queen are playing at all, thereby "replacing" Freddie.
But having the singer from Valensia, or anyone else who sounds more like Freddie would just be inviting that sort of criticism. I'm sure Brian and Roger went ahead with this largely due to the fact Paul Rodgers is so DIFFERENT to Freddie.