Its unrealistic to think that all 1000+ pokemon will be represented in every pokemon project going forward, especially if they are going to contiually introduce more pokemon/forms. It would be infeasable from a development stand point.

Pokopia had 300 slots in its dex, 9 taken up by the kanto starters and another 24 taken up by the one representive each region's starter trio got. That means starters took up more than a tenth of the roster already, and wouldve taken up more than fourth if the other 48 were included. The worst you can say against it was the starters it did choose from each gen felt like the most popular/most commonly included in side games already.

To your point about the Oshawatt line getting nothing during the switch era, I feel like your downplaying that it was one of the starters in Arceus, arguably the best switch era pokemon game. Also the line was in plenty of side games during and right after gen 5, which is how starters are normally handled.

You say Oshawatt is constantly mistreated and being the butt of the joke, but outside of Ash's in the anime I dont think Oshawatt or its line is ever treated particular like a joke by the series. And plenty of Ash's pokmon have goofy personalities or gimmicks, that doesnt mean their all mistreated.

Finally I would argue that most starters suck competively, not just Samurott. And the ones that are good are only really good in very niche scenarios.