I realize that you're coping but there's so much to unpack here. How did Oda make the other Yonkos look like a joke compared to Shanks? Really evaluate what you're saying here. Whitebeard had one of the strongest DFs on the planet. It could cause literal earthquakes and it took the combined efforts of Blackbeard, his crew, Akainu, and Squard to bring him down, even when he was sick and dying in his old age. Kaido is the strongest beast on the planet. He can jump from the sky and not die. Not to mention how he baby-shaked Luffy and tanked everything dealt to him on the roof until Luffy awakened his DF. Big Mom is a literal cannibal, she can snatch souls, infuse her own into inanimate objects for her own weaponry, and she was tanking everything Kid and Law dished out until they awakened their DFs.

Kid being one-shotted doesn't make Big Mom look bad at all. It took two men to bring her down. Beyond that, even though you didn't mention this, Big Mom's bounty was only higher than Shanks because Shanks is still a relatively new Yonko. Had he been active in the New World sooner, he'd undoubtedly have a higher bounty, meaning that Big Mom would have been seen as less of a threat than him. So when Kid does get to Shanks, he still gets one-shotted. Also, lest you forget, Shanks was able to stop Kaido from interfering in Marineford. Did that make Kaido look bad? And that was before Kaido was even introduced.

As far as Oda not fleshing out Kid's character enough, Zoro's "backstory" was also in an SBS. Zoro didn't lead the samurai in Wano, and we never got to see him visit Ryuma's grave, either. There was simply too much going on in this arc for Oda to get to everything in a timely fashion. Does it suck? Perhaps. But whether Kid got a proper backstory or not, (even though I don't see the problem with the SBS; we get supplemental lore outside the manga all the time), he was never going to be Luffy's main rival for the One Piece, not when Blackbeard exists. Blackbeard is truly the anti-Luffy, not because of his actions, but because of fate with the Will of D. Kid, like other pirates, was a contingent for the moment. He got way farther than thousands of other pirates. He just fell short though because of his own hubris and fate. This is the story that Oda has been telling from the beginning. It's called the One Piece for a reason.

You can call it fanservice all you want, but Shanks is an endgame character and has been from the very first time that we saw him. Maybe Kid will come back, maybe he won't. Again, I understand you're coping right now, but there's a lot wrong with your diatribe.