What do you mean? Heroism is still a thing for Alliance, it’s Bloodlust for Horde. Or are you talking about something else?
The problem stems from the inability to easily switch specs.
In vanilla once you chose your optimal talents for tanking/healing, you were unable to do damage in any kind of efficient mana.
As a result, as new expansions came out healers and tanks had problems levelling up as quickly as DPS. Wrath introduced dual-specs, which helped with this somewhat, but they had also started giving healers more damage output and tanks more mitigation/healing.
It’s now at the point where a healer, a tank, and a dps can do basically the same amount of damage. There are groups of people running raids in healer only comps, tank only comps, and even dps only comps, which proves that this has kind of gotten out of hand.
Unfortunately, Blizzard won’t change it, because it’s beneficial to their more casual player base (i.e., the majority).
However, Tank should literally be tanks, not dps. A tank should generate threat and be able to stay alive, they should not provide any kind of healing but they should take more healing from healers. In addition, their dps should be absolutely trash.
In contrast, healers should be super squishy when hit directly, but able to heal through virtually anything and also have pretty trash dps.
DPS should have little to no tanking ability and no healing.
Because the game has strayed so far from that pattern, it won’t go back to it, which means that DPS feel bad because healers and tanks are competing with them due to good/bad rng, raid mechanics and so on.
As much as I love being able to tank elites as a healer, or destroy dozens of enemies at once as a tank and heal myself to full, or not have any downtime as a dps and not need a tank to tank an elite for me, it really takes the role playing aspect out of the RPG.