While I understand your argument. I have my own philosophy for what is retro in terms of games.
For me I don’t look at the system but the games. And for games it about 10-15 years after they were first released.
Enough time that kids can be born and never see this game until now. While I wouldn’t call Pokemon Sun/Moon retro just yet. The 3ds/2ds has games on it that I would consider it retro.
Its been over half a decade since Nintendo stopped making games for it, and even longer since people cared about it.
The only time I will argue something isn’t retro is when its still on the store shelf and not in the discount bin.