I think that one way they could've fixed this, besides giving the different match ups one-two episodes instead of just one, is by simply showing everyone's progress and having them interact in meaningful ways. A theme of this saga is passing the torch, right? Journey's set up had the perfect way to do that:
For Ash's Pokemon, have Gengar be mentored by Ash's Pokemon that were abandoned or otherwise abused by people. Have Lucario mentored by Ash's aces. Dracovish can be mentored by the water and dragon types. Dragonite can be mentored by, idk, the more affectionate ones. Sirfetched can be mentored by the cool and collected ones. Mr. Mime can, idk, be a mime. Devote at least one episode per new Pokemon where they learn a new move after an intense struggle, whenever it's a solo Go adventure, mention that Ash is training at Oak's. This'll give us a reason to root for them during the tournament because we got to see them grow, even if only a bit.
For the Masters 8, have each member do something meaningful with Ash and maybe Go. The reason I and possibly others love Cynthia so much, besides her power, is her mentor like relationship with Ash. So they could've done that. Give Ash a one episode, two episode max, adventure with each of the Master 8, Go and/or Chloe can even tag along. Have each one teach one of the characters something. Lance can teach Ash the true power of the Dragonite and how to bring that out, Steven could've helped Ash understand Dracovish in the episode where it was revived, Alain could help Ash master mega evolution, Diantha could have introduced Ash to Wikstrom so as to train Sirfetched. Iris' episode was fine I guess but one more adventure wouldn't have hurt. Cynthia's episode was fine to but, since her return wasn't really focused on during the episode, maybe she could've helped during the Dialga and Palkia two parter instead of Dawn.
Heck, they could've given Cynthia a villa and had Ash and the Master 8 mingle there for an episode, Team Rocket appears and does a thing that causes a problem, and each member uses their ace to launch an attack that sends the trio blasting off again. The episode could have a moment for each member to shine, making the viewer care about them even more. Obviously it'd be right before the tournament but it'd be something.