I've seen reports over the years going back to his LAD days questioning his stamina/durability to be a full time starter. No idea where it comes from.
Like this one from as recently as last June: However, his lack of durability (and therefore consistency) has repeatedly been an issue during his seven-year Major League career.
There are other similar reports.
Last year was a career high in innings pitched, maybe those concerns are out the window. MLB teams have more info of course so it will interesting to see what happens, given his 2021 success.