Says it all, right there.
If Simmons or Schiff were better candidates, one would've won the primary.
If Castle were a better candidate, he'd have won the primary. Same goes for Norton, Lowden, Tarkanian, et al
You can even go one step further: If Romney or Huckabee were better candidates, they'd have beaten McCain in the primary. And, since they couldn't defeat the weakest candidate the GOP has offered since Alf Landon, they've got no business mucking up the field in 2012.
Anyone can toss their hat into the ring in 2012 and probably will. Reagan lost to Ford in 1976. He took another shot in 1980.