did we all partake of the same story? *squints* because izuku was always katsuki's rival, even long before he got one for all. kats says it himself in his own flashbacks as he dies. izuku has always been that distilled "heart of a hero" he needed just as katsuki was always izuku's "strength of a hero." they are both toshinori's successors, best and strongest together. they don't call them twin stars for nothing.
you're right: their rivalry as it was (predator/prey) is gone because they've come to terms with who they are. and that's a good thing. they see each other as respected equals, which is healthier in the long run. shouto isn't a rival to katsuki because he doesn't care about shouto that way. not lemillion, not mt. lady, not jeanist, nobody. the only person he wants to fight with is izuku, and until that happens, his joie de vivre is dampened.
actually, can we reexamine things? dynamight is NUMBER 5, despite working his tight little ass off NONSTOP SINCE GRADUATION to afford deku's suit. he did all that and still managed to be 5th. AND get a driver's license AND buy a car. DO YOU KNOW HOW HARD THAT IS IN JAPAN????
so excuse the fuck outta you, anon, i think katsuki's doing just fucking fine.
"Since Deku doesn't seem to care anymore, the Bakugo fangirl in me wants Bakugo to not care about Deku in return as well." you clearly don't understand either of these characters. DEKU ALWAYS LIES AND SAYS HE'S FINE IT'S FINE EVERYTHING IS FINE WHEN HE'S HURTING THE MOST. imagine you're born without legs and bullied for it until one day you GET legs and it's everything you dreamed of and more. and then they're taken from you, not all at once, but in pieces, in brutal, agonizing portions, and nobody can help you, and one day, you realize they're completely gone and you'll never walk again. can you imagine that fucking pain? that agony? all your friends going off successful in life and you're left behind because you just aren't living the same life anymore? your best friend has every minute of his life booked up and you've lost him too. i'd rather go my whole life wishing and hoping, than to have it and ripped away from me. i can't imagine a worse fate.
so no, izuku is not fucking ok, and he absolutely definitely cares, but what do you want him to do? run a race with no legs?? he saw the writing on the wall and accepted reality for what it was and tried to move forward and make the best life he could given what he had. considering the amount of trauma the kid went though, i'm surprised he didn't commit suicide by the time the embers of ofa burned out, cause that woulda been the last fucking straw for me i think.
that last page of them flying side by side with smiles frankly tells you everything you need to know about their dynamic, their relationship, and where they're going. izuku always had the heart, and kats always had the power; but when izuku got his power, even briefly, katsuki was forced to confront himself and make his own heart vulnerable. and for that instant, they were equals, undefeatable.
until ofa died, and left the equation unbalanced.
if katsuki didn't care, why the fuck did he get the suit made? he knew damn well what he was doing and how much it would cost and that there was every chance izu might turn him down because he was too afraid to fly that close to the sun again... but he did it anyway, because he cared that much about izuku's dream being fulfilled.
and the equation was balanced again. 2 perfect halves of a whole made one again.