Good for the game, plain and simple.
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Could not agree more mate.
Just to add something i posted elsewhere on this subject.
Currently dungeons, including M+ just revolve around chain pulls and aoe mashing which only goes to further separate classes that cannot perform well in the burst aoe environment, see shadow priest representation in M+ as an example. Now there is still room for that type of zerg play, but it just requires the dps to actually watch what they are doing threat wise and adds another layer of skill to playing your class as well as making tanking a bit harder.
The mark of a good dps from bygone expansions where threat mattered was maximizing output and staying just below the tank on threat, but never pulling aggro and the mark of a good tank was building that aggro to sufficient levels that dps were not taking aggro from you and any that do on occasion you can taunt back in time. Those dps that just chain pull aggro will soon learn not to by being dead all the time.
Now there are those that will cry about this change as they will just see it as fettering there dps spec, but there were abilities that let you drop threat i.e soulshatter for example. I would welcome the return of those types of ability as all it does is add another layer to the toolkit of what is already a much overpruned game to be fair.
In short aggro was never an issue to good dps as they played around and respected it as a mechanic and if it serves the purpose of returning that extra layer of gameplay as well as making tanking more interesting than it is, that can only be good for the game.