this sheer audacity
Disgaea 6 has a setting that can swap between Performance and Graphic mode. In the japanese demo on Switch, it was automatically enabled to Graphics by default, which would slow down everything including the story vn parts. Performance mode has virtually no difference in terms of visuals but the game ran significantly better. But let's be honest, Disgaea 6 is a terrible game sequel of the franchise with a much lower amount of animations (group attacks are just the unit portrait cut-ins flashing for one second), less class units (no nekomata, valkyrie, female healer) and there is a massive inflation of numbers in stats/damage (due of lvl 1 in D6 being the equivalent of lvl +100 in previous games), etc. The performance issues (from the graphics mode) is the least of the worries here.
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It's like how I don't bother with the Dragon Quest trilogy on Switch because it has the kind of visuals you see from the mobile/PC ports of the early Final Fantasy games.
And I could additionally list One Piece Pirate Warriors 3, Catherine Fullbody and Girls und Panzer DX as good Switch ports of PS4 games too, which prove again it's not the fault of the hardware itself but the actions of the dev teams in charge of said ports. Lazy ports happen but nowhere the amount you were describing.