To be fair, Paladins and Bear tanks weren't taken seriously as tanks until TBC, and in TBC both were viable right out of the gate (though Paladins had some effective health problems on a few bosses in SSC and in late BT.) - As a matter of fact, bear tanks were so good they had to be nerfed two or three times before anyone would use warriors again.
Having said that, it's not really the tree itself - by all rights, the prot tree SHOULD be doing a lot of DPS. There's a lot of instant damage attacks, there's a lot of abilities that crit often for decent damage, and the damage production resource (rage) is virtually unlimited in most scenarios - the problem is that we're stuck using really fast weapons to do competitive threat. Shield Slam was a big, hard hitting ability that wasn't based on weapon damage so it was an important part of our dps - that's why this nerf hurts and was so goddamn unnecessary.
The best solution to this problem is to find a way to make it so warriors can do competitive threat with a slower weapon. Another solution here would be a heroic strike replacement ability in deep prot that does more threat based on weapon damage or something. It's not like Paladins have any reason to use fast one handers, and DW DK tanks prefer slow mainhands for threat, so it's not like they couldn't just go back, change all the tanking weapons to 2.8 speed and call it a day.
I think what it really boils down to is every other tanking class but us has some gimmick that increases their DPS, be it unresistable holy damage, high damage diseases + weapon strikes, or huge ridiculous amounts of attack power and unresistable bleeds. I think we need a gimmick like that to be able to compete.