Leaks say a lot things, and are almost always wrong. The idea that you could put a PS4 level of performance in a handheld with reasonable battery life is absurd.
Valve put a damn good custom amd apu in the deck, and it’s limited to 15w if they really wanted they could just slap a higher power limit and get way more performance. But then it would run too hot and it’s battery life would be practically non-existent. And considering that was a partnership with AMD to help design that I highly doubt Nintendo has magically figured out something that neither valve nor AMD new in terms of how to get that kind of performance out of a small power budget