That Sun & Moon episode alone single-handedly destroyed every fan theory about Ash seemingly not "remembering" his past adventures. No, he is not in a coma, amnesiac, physically stuck as a kid or in some weirdly selective isekai: he really is this distracted and this slow to physically change, and his friends are all too available to remind him of that, which incidentally also proves they are his best friends. Only best friends trash-talk you onto such a deep hole in front of everyone, after all.

Isn't that how he got most of his badges from the original league?

From what I remember, it was either out of pity or Team Rocket fucked something up and he helped save the day.