It absolutely is, base weapon damage plus a bit of flat extra as an on-next-hit skill to two mobs is very weak. On top of that you cut off rage income by using Cleave instead of letting a normal auto through.
You don’t have much alternative to be sure, but it is still weak.
As far as Heroics & Kara, which is mostly what we’ve had access to on Beta, threat doesn’t seem like much of an issue. Warriors are pretty great tanks, but there are places they shine, and places Paladins shine.
I’m sure that Druids will shine in later phases, when they have access to better gear, too.
WW is absolutely part of it. Aoe shields, shield spikes as well. Battle shout/commanding shout as well. Then you can also toss a bomb if you are min maxing. I aoe tanked the beta just fine with locks seeding. I did the same on my druid and it took twice as much work.
There is only one AoE tank in TBC. Pallies. Which is why one is pretty much required to do Hyjal.
Warriors (and druids, I assume) do just fine against 3-4 mobs, maybe even 5-6, but any more than that, if they are elite, you need a pally. Or try to kill them before Challenging Shout expires, but that only lasts 6 sec., and it has a 10 min. cooldown.