Are you trying to be intentionally dense here? First of all, open endings themselves aren't a problem since a lot of great anime have them. Gon and Killua had one at the end of HxH, and Gintama's final scene is literally what MPM thinks it's gonna do, have the main protagonists run and say "our journey is going to continue". What makes all these endings work is that it feels satisfying to a long concluded and ardeous journey, something that can't be said for Ash. The first big mistake here was to promote 10 episodes of absolute nothingness as the "beginning of the end" of Ash's journey and have Gary ask that question in the opening trailer as though Ash was going to introspect, while he'll find the answer to that question in 5 mins anyway as we know. If MPM episode 11 was JN137, it wouldn't even have been this awful (still pretty trash but not as bad as it is now). That would've been underwhelming as you put it. MPM is insulting cause it was basically bait to hype the question of "what is the meaning of being a Pokémon Master" while having 10 padded out filler episodes of Ash doing things he's done for 26 years. This series never needed to exist.
(This is the ending of Gintama....feels familiar doesn't it).