It's actually quite simple, the PS4 did everything right (hardware, pricing, features) AND both the competitors made critical mistakes which resulted in the amazing success the PS4 has had. If one of these two factors hadn't been in play, the PS4 would have sold less than it did. It's just as wrong to pretend that the failures of MS and Nintendo had nothing to do with the PS4's success that it would be to pretend that the PS4 sold well only because of the competition failed.
Exactly, history has shown that it takes more than just making a good console to steal sales from your competitor, they also need to make mistakes to make the fanbase switch to the new console.
Nintendo making huge mistakes paved the way for Playstation to become such a hit. Sony making huge mistakes allowed 360 to steal half of the PS2 audience. Microsft making huge mistakes allowed Sony to steal back most of the audience 360 stole.
When the herd loses its way, the shepard must kill the bull that leads them astray.