Amen to that!
I think the Momentum is more of a crowd-pleaser, thanks to the bass and the warm sound. It is very easy to fall in love after a short audition at the shop, and make an impulse buy (As it happened to me).
It is easy to dismiss the P5's as they certainly have a colder signature, and less bass. A colleague of mine said he preferred his £20 headset over the P5's because they had more bass - He recognized the P5's had more details, but was not willing to pay extra for that. Also, he didn't know what I meant by "punchy bass". Now, he listens mostly to Dance MP3s tunes, so clearly, his focus is different (Bass bass bass... And more bass please!).
My point is, dismissing the P5's as rubbish is idiotic at most. At this price point, neither will offer the perfect sound and you will have to go with whichever sounds best to you.
Funny thing is, both my GF and I loved the Momentum after hearing them at the shop, and we both thought they would kick the P5's arse. We both changed our mind when we compared them at home side by side. Our AKG 701 is still our preferred one, but none of us dare to wear those in the street.