Hiii I love your posts! Especially the analogy about daisuke, taichi, taiki and tagiru. For the DXW I wanted to ask your opinion, if you think tagiru actually surpassed taiki, I mean the show indicates that he did but personally I'm not convinced lol
In essence, I think the fact that "superstar" was defined so vaguely is intentional. Tagiru is a pretty self-aware person, and he seems to be perfectly aware that he's the one who determines whether he's satisfied with himself. (I just wrote a meta on this!) So in other words, the one who gets to decide whether Tagiru has surpassed Taiki or not is Tagiru himself -- and I would say that probably applies to "surpassing Taiki" too.
Tagiru wanting to surpass Taiki can mean a lot of things. It can mean anything from "becoming beloved and accomplished in every way above him" to just "doing one really cool thing better than he did at some point". So one can argue that by being able to wield the Brave Snatcher on Taiki's behalf and save the world with Gumdramon, Tagiru surpassed Taiki that one time, because he did something Taiki couldn't. Next time, maybe he'll try to surpass him in basketball! Nobody ever said surpassing Taiki was just a one-and-done; Tagiru just thinks Taiki is a good reference point to use to motivate himself.
And besides, I don't think surpassing Taiki is Tagiru's only goal in life. Even if Tagiru thinks that he's fulfilled his Taiki-surpassing quota(?) with the Brave Snatcher and doesn't need to continue pursuing that angle anymore, it's probably just going to be like "Yeah! I did the cool thing! Time to pursue the next cool thing."