What does DI have to do with anything? It was hard to find a sp, boomkin or firemage in 10man or 5man, that's why they changed it.
In this game there is plenty of solo content if you don't want to depend on other players. However, raids and dungeons are supposed to be a united/common effort to defeat a challenge before you get the reward.
The only current mechanics that change a patchwerk rotation are: switch target and continue with your rotation, aoe, dps while moving and/or keep your dps cooldowns for a burn phase. That's pretty boring to me, and the boss mechanics tend to be more and more repetitive.
If you run a group, be it raid or dungeon, with an unexpirienced player or just one that sleeps/sucks, isn't it normal if something doesn't go as planned? I'm saying it again and I won't repeat it anymore. Pugging could be fixed so that threat would have a lower impact, but if the tank freaking sleeps, then yes, you should overaggro him. Why is it that other classes being unexpirienced/undergeared has implications, but a tank should hold aggro while watching TV, while you nuke the shit out of it?
If you don't PUG, then you should group with similar skilled players, in which case threat should not matter much, if at all.
I guess you are too biased to imagine a game design where threat plays an interactive role.