We can't ignore pain like a Warrior, and we don't have he health of a big ol' bear. We aren't as scary (threat) as a Vengeance DH or a Bloody DK. But I've yet to tank content where my class was a limiting factor. It feels like we have just enough of everything to be in a sweet spot: we may not be the best tank for the instance, but we're pretty good at all of them.
Disclaimers:
1) I main a prot pally so I'm obviously biased.
2) I have raided on most of the tanks, but have never played a BM.
Also note I am not debating whether a skilled player can tank M+15/mythic EN on any of the classes, certainly not here to claim that I'm an elite player; my point is merely that Protection Paladins are in a happy center between the pros and cons of various tanking classes.