I disagree on almost all points. LIke them, love them or hate them, both are nothing more than pop artists that appealed to the masses. They aren't any different than the Beach Boys, the Beatles, Elvis, or any number of other highly successful artists over the years.
The Beatles weren't always "classic rock" and a lot of their early stuff was extremly POPPY. That doesn't make it bad, but it is a fact. They borrowed from those that came before them just like many artists have borrowed from them over the years.
Artists don't have to "grow" and "evolve" continually to be considered "real musicians/artists". Pop music appeals to a different crowd than other types of music. Don't like it? That's fine. I'm NOT a big defender of most pop music because I don't care for it, but the two highly successful acts that you mentioned will always be revered as among the best in the pop music realm and for good reason, NOT just because they embraced the potential of fame.
I DO think that nearly anyone who gets into the music business on a national or worldwide level has a desire for fame and fortune. To say they don't is very naive. Some can handle the fame, others can't, but none of them are there because they don't want anyone to know them.