No, it actually is pretty true. Inner Beast alone is a huge trump for a Warrior over a Drk. Warrior feels squishier overall simply because they don't have a raw mitigation tank stance like Drk does, they take more damage, but they get healed for more. Their HP is going to fluctuate a lot.
You can keep Storms Path going simply whenever, that's a permanent 10% damage reduction for everyone that doesn't rely on a parry to apply, meaning you can have it going when you actually need it most.
You can have Inner Beast on standby for when you need it consistently.
Raw Intuition is a 100% parry rate from the front, essentially a Rampart for physical damage. (You should never be getting hit from the back or side in a raid anyway)
Equilibrium is is a crazy strong potency heal they can use every 60 seconds which does exactly what self healing needs to do for it to matter; burst heal. And in Deliverence, well, good luck making a Warrior run out of TP.
Then you have Vengeance which that has a SHORTER cooldown and a LONGER duration than Shadow Wall.
And then the usual cross class stuff that all tanks have. Not to mention, a lot of their cd's generate wrath, meaning even more IB uptime.
So when it comes down to it, Warrior feeling squishier than a Drk is an illusion. Their HP fluctuates, they get hit harder outside of their cd's, but get healed by more per heal, they've always been like that. Any Warrior that feels squishy with his cd's even, is likely not a very good Warrior, because with a CD up they essentially have a Drk's passive mitigation, with more damage, that also receives more healing, for their cd's duration. Thing is however, a Warrior can keep things in cycle almost like a Paladin can at this point, and when there are downtimes, Wrath is a static thing so long as you are in Defiance, and failing to have Inner Beast when you need it is a sign of a bad Warrior.
Warrior is far more 'developed' than Drk is. And that makes them very efficient OT's, and MT's for many fight. Any fight a Drk can MT, a Warrior can do better while bringing far more to the table in what they can do for both themselves, and the others in the raid group. Hell even Paladin as well, because neither of them are selfish tanks by poor design.
But even still with all of that aside, Drk can do many things, I have all of Alex down as a Drk, and even did the last floor with 2 Drk's. Sure it was hell, but an all magic fight like that is where it feels as if Drk is suppose to shine. Yet they don't, because in an all magic fight, you may as well take Reprisal off of your hotbar. If you have a monk, well there goes the only other thing you actually contribute to the group with.
tl;dr: Warriors being squishier than Drk is an illusion, or a sign of a very bad Warrior.