It absolutely counts as 3 damage. No argument there, the rules say that exactly, but do you actually add the damage? If you remove a condition maker that counted as 3 damage, you then add 3 damage tokens to the creature? This seems wrong. Also not sure if finite life really matters. The damage Taint counts as already can't be healed or regenerated, and were not adding life, we're removing a poison condition that counts as 3 damage.
I hate to challenge the great Zuberi, but I feel like an official ruling is needed here.
Taint feels like a 3 damage marker always under the effect of finite life