In vanilla WoW mobs used to flee at low health, it was later scrapped because according to some internal research this panicked windowlickers that didn't know what to do. I remember when warrior tanking I had to occasionally swap stance to Harmstring a runner, because the mage frost nova was on cd. It added another element to the gameplay and this, for a tank that had no AE skills whatsoever in defensive stance, made the gameplay very engaging. Thunderclap required battle stance, so it was a pain to use and it didn't generat much threat anyway, so it was normally used to open a fight: charge, tclap, swap to defensive stance, battle shout and the single target sunders for the win. Threat was not guaranteed, you had to work for it, so you could reliably control 3 or 4 mobs, you needed to have support and cc.
Regarding support in modern games, you are right, it doesn't work in groups because it slows down and the contribution is not measurable. I for once, liked the Rift bard, it did some damage, it provided good boosts to the party, but in one-group content, it was honestly subpar compared to a dps build and it showed.
Even a game like GW2 that potentially was a good ground to utilize support classes, ended up being all dps doing speedruns.
The concept of speedruns alone is in my opinion out of place in a MMO, but apparently some people have a hardon for them. One thing is trying to stay ahead of respawn, one other is skipping 80% of the trash, but I disgress.
Old EQ had a different issue imo: the only person who was always playing was the puller, the others took turns at hitting their 3 or 4 buttons (if those many). It was a chat with dragons with the occasional messed up pull that kept everyone awake.