Thats the BIGGEST issue with dps im running into haha especially in LBRS and UBRS, I hate when a mage AOE peels everything off me but doesn’t have the DPS to pull it off, so they’ll ice block then they peel onto the healer >.<
Really is just communication haha, I mark things with skull but yet the DPS seem to feel good going after a unmarked mob while im still tab sundering haha.
Theres better places to spent talent points? because threat?
It’s pretty much impossible.
I was doing Uldaman the other day and it was so frustrating. Particularly by the later part of the dungeon when groups start getting bigger, holding aggro is absolutely impossible.
You’ll end up running after lost mobs and taunting no matter what. Real tanking seems to be reserved for raids. 
Make sure to cast bloodrage after combat start - the instant threat gen from gained rage is helpful, then i usually demo and battle shout, demo again, then tab sunder/revenge - dont waste rage on shield block unless you NEED to survive - with the amount of mobs hitting you the buff will drop instantly. Save taunt for the highest hp mob that is heading for your dps/heals and continue to tab sunder/revenge.
Dont do anything on the same target twice, including auto attacks - for example: sunder, tab, sunder, tab, revenge, tab, taunt running mob, tab, sunder, tab, sunder, tab etc etc
Make a paladin so you can be a real tank.