You got a weird case.
I mainly heal (SGE) but also tank and DPS, casually mind you, but I've taken several characters to End-of-Content as SGE-WAR-DNC.

In your situation I would just silently ignore a tank that was trying to tell me how to heal, and do the best I know how to prevent a wipe, even if it means letting the tank die. I've done low level dungeons in Duty Finder after having lost a tank, so even a poor tank can usually be worked around.

Worst case, though: I was in Aurum Vale, got a totally incompetent (or totally trolling) tank who ran around kiting Coincounter and eating all the morbal fruit, so after one of the DPS quit, I quit too. That's one situation the quit option is made for.

But usually, the tank is good enough, and sometimes they are spectacular (except when they're me )