That's the trouble, though. There's been plenty of people who have been "exceptional" in one class and not impressed much in other series. Roger Lee Hayden, James Toseland, Kenan Sofuoglu, Toni Elias, the list goes on and on. Checa and Biaggi, WSBK champs, who couldn't cut it at Grand Prix level.
The problem is that you first have to get in to MotoGP before you get a shot on a decent bike. If there's only 17 bikes, or 14, you're never going to get a shot. If there's 21 or 24, you might get a shot.
Your arguments sound like the idealized world that economists love. The rational, optimizing .... economicus has proven as elusive as the GP series you seem to be describing.
couldn't cut it? as far as the first three you mention i agree, and chuckit....well, but biaggi... really. if you remove doohan first but mostly rossi, things would have turned out alot different for old max. i know its all just if if if but seriously biaggi was better than the rest for the most part and would have been champ on a couple of occasions..... and i'm no biaggi fan.