I don't think we talk about Rose and Leon's final interaction in Pokemon Evolutions.
In my opinion, Leon gets a lot of almost unnecessary hate. I know a lot of it is centred around him constantly being called unbeatable but there are two things to bear in mind with this: a) Galar hasn't seen another champion for about ten years now, of course there'll be a lot of hype around any champion who can keep their title that long, and b) the mention of him being unbeatable almost every five seconds was probably intentional by the writers to make us as the player want to take him down just so people would shut up about it.
And Rose probably would have been happy to keep up the hype in universe (either game or anime, there's very little difference). After all, this is his prodigy, his trophy. And why wouldn't you in that position? Your region hasn't had a different champion for a practically a decade. The pieces are too perfect for your plan. If someone can't be beaten for ten years, then Eternatus - the very thing you're raising that champion for - should be no problem. Best of all, Leon's been, well, obedient for you. He's turned up to all his public appearances, he's given everyone something to look up to, to praise, almost worship. What does it matter if you release a god of a pokemon? Leon will handle it, promote your idea and all will be forgiven...
Now, this next bit is a bit of speculation about why Leon went along with Rose and his life before. In the game, we only see his mother and grandfather. In the anime, we're told that Leon didn't really have friends at school, either because he was too busy training or he was helping with Hop. So it's fair enough to assume that his dad wasn't really in the picture - either because he was dead or just left (I have to assume the latter as we don't see any sort of memorial or grave for him) - as we never hear anything about him. Presumably, Leon had to play the second parent to Hop as his mother either worked through a breakup or divorce. Sonia's line is 'busy taking care of his little brother'. Notice how she doesn't say 'helping', this implies that Leon was doing a majority of the parenting because of how depressed his mother was. Hop never mentions their dad either, considering the only one he wants to make proud is Leon, so he probably can't even remember their dad. So yeah, Leon had to take up the role of 'father' before he was ten.
And this would play right into Rose's hands.
Your ten, your father has left you and he's not coming back, you're almost constantly doing most of the parenting for your mother. On one hand, you want to shine so brightly that your dad will have no choice but to come back and at least acknowledge you. On the other, you don't want him to. This is all his fault. Then, when you become champion at ten, the chairman himself takes interest in you. You don't have to be a father anymore. For once, you can be the child. And that's how it plays out for a few years. That is until you win every match. Rose fills your head with ideas of greatness, being Galar's shining light. But for some reason, he won't let you go home except for brief visits for 'champion reasons'. You find you have to make more and more public appearances and sponsorship deals. But, deep down, the child in you wants to make your father figure proud and, even now, you do too. So you do everything right. By now, the mantel of 'champion' feels more like a burden than a point of pride. But you continue to hype up crowds. Even if you can no longer go out in public without the press.
You notice a few cracks in Rose a few years later. He's been talking about 'infinite energy' and 'the greater good' a lot more than he used to. You have your doubts but years of being Rose's son - even if neither of you said it - crushes those doubts. Surely he wouldn't do anything to put anyone at risk?
That's when pokemon start going on dynamax or gjgantamax rampages. Lives are in danger and you do all you can to help. But you see things that you doubt will leave you - people's houses are destroyed, sometimes with their owners still in them, there are multiple injuries and families torn apart. Eventually, you decide enough is enough, it's time you see for yourself what Rose has been up to in Hammerlocke. You watch for yourself as Eternatus emerges. You follow it up to Hammerlocke stadium, where Rose is waiting.
"I find talented Trainers like yourself and help you advance. Yes, and now you will catch the revived Eternatus." [Pokemon Evolutions: Sword and Shield... From Here To Eternatus!]
You realise that you were never worth anything to Rose. You'd been nothing but a cog in his machine. He didn't care for you. At least not as much as he cared about what you could do for him. You no longer care for his sob story.
"There has already been great loss! I don't want to see anymore tradegy!" [Pokemon Evolutions: Sword and Shield... From Here To Eternatus!] You burst out. You will catch Eternatus. But not for Rose. You will catch so it may never see the light of day again. You can no longer care for Rose and the rest of your days are spent trying to work out who you are without the champion he raised you to be.
