If this were to actually come down to a matter of categories, rather than playflow, shouldn't we note that not even one of those is unique to Healers/"Supports", though?
And, heck, Chain Strategem is merely a worse (in being limited to a single enemy target) raid buff.Tanks have external and internal mitigation. Melee DPS have internal mitigation.
Most DPS have external buffs.
All debuff enemies.
Most can technically heal.
All can damage.
Most Magical DPS also have rez.