So after playing TBC again and comparing it to legion I've made a few conclusions.
Besides the tank, every one in the group had very few hp. An elite mob could kill a healer in one or two hits.1. People had far less HP
This was also an issue when questing outside. If you would pull more then one mob you probably would be killed right away. This is why murlocks were quite a pain since they would spawn close together and you could easily pull more then one.
The only class that could reasonably AOE tank were paladins. Most guilds had one paladin tank to aoe the trash in instances like Mount Hyjal. But you would have to give them quite allot of gear to be able to survive. So the number of paladin tanks on a server were quite low.AOE tanking was not a thing
Warriors could aoe tank to some degree that is true but only skilled warriors were capable of maintaining aggro on 3+ mobs. And even then you had to dps the target the warrior was focusing on or else youd risk pulling aggro (and remember what i said about mobs 2 shoting people).
Pulling aggro off a warrior would mean that now he would have to run around and chase the add that is in the raid and would not be able to build threat on the two other adds that people could still be dpsing.
This is why people marked targets and CC`ed some of em . You had to do a kill order so that the warrior could focus building threat on the target that was dpsed down.
Grouping targets up and aoe-ing was not possible back then.
In wotlk most tanks got aoe threat generating abilities and thats when the tactic of grouping mobs up and aoeing them down became a thing
While sheeping or banishing one mob was not difficult. The problem comes when you have to remember to resheep the mob. As i said people had very low HP and you could get 1 shoted by a sheep that broke. Thus the mage had to constantly keep an eye on the sheep timer as well as his rotation.3. CC-ing was a thing
Even worse the sheep could break if the warrior tank would use thunderclap next to it, or if some one would pop an aoe next to the cc mobs (happened more then it should).
Most packs required two or three sheped mobs at a time and things could of went wrong quite rapidly
While there were a few aoe healing spells (chain heal) most healing was done with direct spells. Aoe healing costed allot of mana and in the first raid tiers up to sunwell and black temple, you just couldn't afford to spam aoe heals.4. Very little aoe healing
Thus people had to be very careful not to take damage when they shouldn't.
As a dps the healers would most likely skip over you as they had to keep the tank up. So you mostly had to deal with damage yourself.
Allot of guilds were using first aid especially in Tempest Keep and SSC as you just could not afford spending healers to heal the raid.
Now a days every healer has some form of aoe healing and first aid is quite usless.
As i mentioned before threat was an issue. A tank had to keep threat on 2-3 targets at a time in some cases. As a dps you also needed to know what target you should and what you shouldn't dps or risk pulling aggro and wiping the raid.Tank skill
It was the healers job to keep the tank up and a good healer could pride himself on the tank never dying
It was the tanks job to keep threat and survive by avoiding damage and poping his cds at the right time.
While addons and people did improve since tbc , we have to be real that the game was different back then. Most of the abilities that are available now did not exist in TBC and the total HP of people made it very difficult to survive most mistakes.Conclusion
I kinda like the game back there more as there was more comunication and coordonation required to kill trash and there was also a sense of strategy required while questing solo.
now the trash is mostly round em up and aoe , a boring grind that serves no purpose rather then to take more time to complete an instance