Yeah, but there's also a reason that the "american era" is considered a "golden age"...
To compare like with like, you really should put the 'factory' qualifier in there.
Ago, Hailwood, Lawson, Rainey, Rossi, etc. were factory riders from the get-go. There have been very few instances since 1949 where a non-factory rider has gotten a foot on the step.