Hiya.
Here's a log from a 60 roulette where the tank actually had considerably less HP than I did.. The log has me as having a bit over 17k HP, he had less than 14k total. It's worth nothing that he did use his cooldowns though.
I cast 49 GCD heals with further 12 oGCDs out of 428 casts across a ~19 minute dungeon.
That results in a heal roughly every 20 seconds, and a 7 to 1 ratio for dps/utility to healing.
Note how close that is to the example I provided in your other thread? It's because irrespective of how little gear your tank has, the incoming damage is pretty similar all told. Cooldowns have a far bigger effect than gear here. The difference is that I simply had to weave in more Adlos to keep the tank safe through bursts of damage. It certainly didn't stop me from DPSing though, and it shouldn't have prevented you either.
You literally only have yourself and your potential lack of awareness to blame if you let these situations get the better of you.
Also note how we didn't get salty and kick the tank at the first opportunity, it was hard work but I relished the added challenge.