The honest answer to "is the Ninja Woodfire as good as a Traeger Pro 575?" is no — but the question is wrong. The right question is: what kind of cook are you, and which appliance fits that cook?
If you smoke a brisket once a year and grill burgers 50 times a year, the Pro 575 is overkill and the Ninja's grill function plus air-fry will serve you better. If you smoke once a month and feed crowds, the Ninja's 141 sq in will frustrate you within the first cook and the Traeger's 575 sq in is the only sensible answer.
The trap is buying a Traeger because it's the prestige brand and then using it for weeknight burgers — at which point a $370 Ninja or even a $200 Weber Q would have been the better buy. Buy the appliance that matches your actual cooking, not the one your neighbor has.