I always carry Kairyu with me
Sawyer, Gladion, Alain (imo) were good rivals, even better than everyone before Paul (yes, even Gary, who almost never showed up), what happens is that Paul set the bar very highTokio should've been the first since he's so integral to Go's character but of course he never appears again le sigh.
Honestly I forgot all about the lack of rivals in this series because ever since XY they've been introducing them later and later and much less of them. Heck SM really only had Gladion and I guess Hau so maybe there just being phased out as prospect of having a 3-4 year spanning rivalry with slow buildup stopped being appealing to them by the time Trip rolled around
The opportunity was lost in BW, N must have been Ash's rival from a philosophical and moral point of view like in the games.