It's also very dependant on other people. It tends to average out over time, but if you have bad luck, it can seem like it's impossible to keep people up because it may very well be. Stuff in Bardam's hits like a truck if the tank isn't using gear from Bardam's because there is a huge defense stat spike. Ala Mhigo has a couple of mobs (like the Avengers) that hit surprisingly hard and if you get a huge room pull can turn into a mess quickly. DPS can help or hinder you. Tank cooldown usage is pretty important.

There's always more that we can do to heal better (except the top 1%, maybe, but I'm sure not in that group!), but that doesn't mean its all on you. If you get a run where all you can do is spam Cure 2 to keep the tank up, then do that. It happens sometimes.

You're on my data center, so if you want to try running together sometime, I can tank one of the ones you have trouble with and see how it goes.