Are they? Casey programmed the walk monster for Jon's game, a brute force tester to make sure you could always walk both ways and never get stuck, instead of building the walking system using a nav mesh. There was one place you could walk where you weren't supposed to, despite the walk monster, that would have been obvious if it was a nav mesh.
John Carmack is a legendary game programmer. If I can identify a superior algorithmic approach to something in Doom, does that disqualify Carmack's credentials?
First I think I'd want to see you identify a superior algorithm known when Doom shipped and then we can have that discussion about who's credentials should be disqualified.
I’m sure you can find bugs in the work of any game dev you would consider legendary, game implementation is generally very messy