Kawhi's legacy will definitely take a hit here.
I don't think Kawhi's legacy takes a hit, he's already a 2x Finals MVP. You can point to poor statistical performances in close out game losses for a lot of all time great players that nobody thinks about now.
But I do think Kawhi had a chance to take his legacy to the next stratosphere. It could have been 3 championships by age 28 (technically he's 29 now, but this is only because the season was delayed). That's ahead of Jordan, LeBron, Bird, Curry. Shaq. And to do it with 3 different teams, 2 of which could have been in back-to-back years, that would have been incredible.