I mean its not like this is The MangaSounds like Pokemon Company should take a note from the anime and, instead of having one manga-ka work on all of them, hire a different one whenever a new gen/game comes out.
And yes, I realize what I said is probably blasphemy because the magna has a heavy amount of lore & continuity, but if Hidenori Kusaka is having a hard time keeping up due to the the insistence of releasing a new game/content each year, plus his health is a concern, I say its better to make that leap now than waiting for something worse to happen to Hidenori Kusaka (which may or may not have been caused from trying to keep up with all the Pokemon stuff). Obviously I'm not implying to drop him, infact it would probably be wise to involve him in choosing new authors as they'll have to share notes and better to do that with people who are familiar with each other (even if they only met during the interview process). If they find someone who can match Hidenori Kusaka's style he could even give them the plans he had for the series that are still waiting to be finished and focus on the ones he wants to personally work on (which would hopefully be better for his health as he could work at a more manageable trait).
There's always been other mangas, and they've never really pushed any of them; there's a few statements from a few Pokemon creators for Adventures but that's about it (& probably more because of how long its ran and relative fan base). Otherwise there would probably be Adventures arcs for Let's Go, Arceus and SV going right now alongside USUM & SWSH.
Adventures has also already had author & artist changes through the years iirc.