I think all these guys feel they have something to prove until they retire. I think he feels great about his two titles and now he is trying to do it in a little bit more of a solo role. Just like Lebron, he has a shot to get one or two in a different way and then he will be 4 time champion, not 2 time champ with 2 asterisk titles.
I do think Giannis' title will continue to be more impressive, but he was like a millimeter away from getting bounced in the second round by a KD team that had almost nothing else. Will people remember that the Brooklyn team would have likely beat the Bucks if Harden or Kyrie were healthy? Should we put an asterisk on that title?
Did those titles and finals mvps solidify his standing as a top 15 NBA player... probably not. If he won no titles staying in OKC (as he would have since everyone says GS was an unbeatable juggernaut even without KD) - then his resume is waaaaaaaay less impressive. Stacked team or not he went out against the second or first best player in NBA history and won... he hit the key shots... he was the best player on his team. Is CP3's legacy more impressive? Will KD be remembered as a better player than Chuck, Mailman, Ewing?
Winning a title is hard/impossible... almost all title teams are stacked... some more than others but Magic, Bird, etc. aren't ding'd because they did it with the teams that drafted them. I mean is KD, Steph, Green, Klay way more stacked than MJ, Pippen, Rodman, Toni Kukoc with great role players like Harper, Longly, Kerr... It wasn't guaranteed to be a championship either... remember when prime Lebron, Wade and Bosh lost to Dirk?
It wasn't a waste of time and it will help his legacy to have the titles... even if the degree of difficulty isn't good enough for some.