I am a little confused by these complaints as well, as I suppose I'm on the "nothing has changed" boat.

In 2.1 I lost agro when
A) A Dps attacked before I did
B) Healer regen before a pull and I didn't notice
c) There is no C

I never had to fight for agro... ever... I just tanked the mobs with my rotation. It's the same now, except my rotation is different.

I suppose Paladins might have some room to complain, being that they got an enmity buff and nothing else to do, but even that is kind of... well... eh. Paladins could hold agro in 2.0 by just spamming Flash, in 2.1 it's the same deal except you have room to do more things (like Riot Blade? I honestly don't know).

Holding enmity was never super complicated or hard, I don't really see what super in depth enmity holding tanking sub-game we lost.