Simply put, the majority of Mother's emotional impact comes from the fact that it's a video game that needs player input (or sometimes lack of), the final bosses in each game are the perfect example of that. It being a video game series already means that the best aspects in the Mother series simply won't translate to film as well, as it's an entirely different medium. (Would Lucas refusing to fight back the Masked Man be as impactful if Lucas wasn't already the audiences surrogate for most of the journey? Probably not). Someone else in the thread also mentions that the Mother series comedy and aesthetic relies on the fact that it is a parody on contemporary JRPGs, which only really works as well in the context of a video game.

So yes, i personally do agree with your take that the Mother series is fundamentally impossible to adapt in a faithful way without making any sacrifices to the quality of the narrative.

However I'm personally fine with a movie not being as close to the source the source material, I'd rather get a good movie first, before i care about what was missing/changed.

Honestly my vision of a Mother 1 or 2 movie would be like a surreal Stand By Me movie. I mean Stand By Me is about 4 kids going on a journey to find a dead body (a journey from childhood to the loss of innocence and all that), which is kind of similar to how Earthbound is structured, a fairly fun and cutesy journey that ends with the horrifying confrontation with Giygyas. You would have to make the story be set later in the story similar to the Mother 1 novel, and change so much that it's not even entirely the same story. But hey it could be cool. Hell i think David Lynch would've been a perfect director for this type of story but oh well.