In my view, that definition of “Tanks” comes from MOBAs and RPGs.
And that “Tanks” also known as “Heavies” in Class Based Shooters, all uniformly have significant firepower.
And considering the game is at a point where you either need to convince more DPS player to play Tank, or the entire game dies. Going to MOBA/RPG route would be suicidal for the game’s finances.