When I heal I just let the tank decide. If I feel he/she is pulling slow for what I can handle I will mention something but I never push them to do it. You do you, I'd rather have the group comfortable and get it done than wipe because of avoidable things. But when I started tanking I got to lvl 50 doing normal pulls for lvling which was smaller pulls at 50 I entered my first 50 dungeon told them I was new to tanking and I would try my best. Did the pulls normal for manor HM which is to the locked doors. Got to the last floor and healer tells me "stop pulling like a pussy, pull it all." I knew we would die but I did what the healer asked and we died, not because I lost aggro but because they couldn't keep up with the healing. Even as a new tank I knew my limitations and not having high aoe damage I knew my groups limitations. Work as a group not individuals and you will be more successful, look at your group comp it's so important.