I would’ve thought this:
He was the best known cyclist of his generation
could imply he was the ‘best’ of the ‘known cyclists’.
ie: Many cyclist’s were known, but he was the best (cyclist) among them.
But could equally be read as best known among a group of cyclists. There’s some room for ambiguity in interpretation even if in the strictest literal sense if means what you say.
Where as this:
He was the most well known cyclist of his generation
most definitely says he was the one that was best known, but not necessarily the best (cyclist) of the lesser known cyclists.
Or have I got exposed my own misunderstanding there?