Thiem is really a member of the LostGen, born in September of 1993. I know my year ranges aren't official and also rather artificial, but I see Lost Gen as those players born 1989-93, with NextGen 1994-98 (this would technically fold Shapo and the Little Minotaur in with kids like Aliassime and Draper). In other words, after Cilic/del Potro (both Sept, 1988) and before Pouille (b 1994), although in a way 1994-95 are more transitional, with 96+ being the heart of NextGen. Lost Gen being: Nishikori, Raonic, Goffin, Dimitrov, Tomic, Sock, Thiem, etc.
In that sense, like the others Thiem is in danger of being skipped over by younger and more talented players. Rafa's resurgence in 2017 probably diminished his chances of a Slam more than any other player. But he is only 25 and has a solid 5+ years of peak level, maybe more given today's context. He may have a chance to sneak one in.