That is a pretty bold prediction.
Sure, it won't sell as well as the PS1/2. But that's not what you're predicting here. You're predicting that one of the Wii U, Xbox One or 3DS will do better. Wii U isn't really worth mentioning. Xbox One I can only see happen if a huge number of people get the Xbox One X and Series X mixed up. I suppose you should never underestimate the stupidity of people, but still... So that just leaves the 3DS, which IIRC dropped pretty hard after the Switch launched.
The only way this would be an "extra easy" prediction is if you're including the Switch as one of the 8th gen consoles. In which case, yeah, I could definitely see the Switch selling more post-Nintendo 9 launch than the PS4 does post-PS5 launch.