Really? Name them. Riders who won more than one championship and then faded away. Remember we're talking about MotoGP/500s here, not the sub classes. One championship can be had with the right confluence of rider, bike, and circumstances (see Nicky, KRJR) but two or more? Not hardly. Go through the entire MotoGP era and you have 5 champions: Rossi, Lorenzo, Stoner, Marquez, Hayden. Hayden has one, so he doesn't count. Marquez has one, soon to be two. Lorenzo has two, but he's still racing. Hasn't faded away. Stoner I guess you could say "faded away" by retiring. Go back to the 500s, maybe you could say Freddie Spencer faded away after winning two 500 championships. So if Marquez only wins two championships then he's only as good as Spencer or Stoner, right? And nobody's heard of them.
Saying "it's the bike" is ......... People said the same thing about Rossi when he was on Honda. See Biaggi. Biaggi got a Repsol Honda and couldn't beat Rossi. Biaggi was wrong. So is everyone now saying that the bike is the reason Marquez wins.
You don't win a championship as a rookie and 10 wins in a row without prodigious skill and talent. I love how everyone wants to minimize Marquez's work over this year and elevate Rossi to his better based on one race. Rossi could win the next three races and Marquez could sit out the next 3 races and Rossi still wouldn't be leading the championship.