You say the anime is against game rivals but SM is the first season since OS to actually have the game rivals be the main ones. Heck even in the league there isn't an OC meant to be the dream crusher like the past ones
Well it's not like they had a choice, those two rivals just happen to be related to characters Ash met. And with such a large cast it's easier to just use Hau and Gladion as they don't need to spend much time introducing or developing an OC. Still sucks they took away Kiawe's rival card though....
I won't be surprised if they go back to using OCs come gen 8,
especially if Hopp is the only rival. But if we do get one, I hope it's a girl trainer for a change. It's so annoying how the other characters(May, Dawn, and Cilan) are allowed competent rivals of the opposite sex, but not Ash. It'd be a fine way of changing things up... though I'd just settle for the rivalry being an actual rivalry like Paul and Trip's where Ash has to fight to earn their respect and not instantly have it like he did with Sawyer and the Stu cause everyone in Kalos worshiped the ground he stood on.... like certain fan fics
That's why I like Guzma being portrayed as more of a rival, he didn't start off as Ash's friend and much like Paul and Trip doesn't share the same views. It makes me a bit hopeful that his main rival can be more along those lines and not his friend like in XY and SM.
I do love Gladion, but they shouldn't have made him so quick to bond with Ash. Hau being Ash's friend immediately works because Hau's that type of character, he instantly becomes Sun/Moon's best friend in the games despite them just moving to Alola.
Heck with Galar being so battle oriented, I'd love to see a rival with a
massive ego. That'd be quite fun. "You think your Pikachu can take my *insert fully evolved Galar Electric/Yamper's final form*? Ha! Get lost, kid!" "Ha, told you! Now if you excuse me, I've got a date with my fan club!" "Yeah, I'm the greatest trainer! Leon's not going to stand a chance when I face him!" "I-I lost? N-No, I was distracted! This battle doesn't count, my streak continues!" "You dare try and steal the future champion's Pokemon?! Corviknight, make an example out of those clowns!"