For resto yes, but Guardian still has 59% armor in my set, 20% dodge, -25% from all magical damage so it is very viable even after stacks. With the ability to juke people with wild charge (extremely effective btw), I would say a good Guardian and a good Prot are pretty much in par. Travel form leap works with stacks too, so you can actually move from place A to B quite a bit faster than a prot, and kite more effectively. Bear charge roots opponent for 4 seconds, which is very good and druid also has a 3 second stun ability that deals ~300 damage non crit (100 per tick), but you can not move during the effect. Guardian is very viable, but same as with prot, without healers you wont go too far with the flag if your team isn't totally clueless.
Not saying that prot is bad by any means, Balthasaur proved today it is very viable spec for fcing if you know what you're doing. And just realised this thread was about warriors, sorry for the off-topic!
Just my thoughts