There isn't a reason for NX to be weaker than the PS4

[Miyamotoo]

There is always some reasons:
-Expansive gimmick that effect on overall price of console so Nintendo cant include stronger hardware because console is already expansive because of gimmick (this is basicly Wii U).
-Nintendo wants to have very affordable console ($200-249).

I personally expecting that NX will have similar power like PS4 with price point of $299.