I'm not a big fan of "Educational" non-healing, but the GMs treat that sort of thing as a "difference in play style" and it's probably not going to go anywhere in a complaint. Especially when there are completely legitimate reasons for a healer to de-prioritize healing someone, even a tank.
I've had the healer I run with stop healing the tank and focus on the dps and herself in runs before when the tank wasn't holding threat, was standing in things, and wasn't popping CDs to mitigate damage. It's rare, but it happens.