Why do they try to make tanking harder?

[Archona]

Healer should be fine DPSing in Cleric Stance, though he shouldn't let you die. Potions are also a nonissue, if you have them and want to use them, sure, if not, then no biggie.
DPS pulling off of you in low level dungeons is not a big deal.

You're probably not using Flash often enough, aren't marking targets, or aren't switching targets often enough.

Important part about tanking is maintaining pace in dungeons. If you're too slow then you may be incompatible with your party members, which leads to things like DPS pulling in front of you.

Letting your party die is just proving to them how bad of a tank you are.

edit:
Just an FYI on healing:

Newbie healers are worrying about keeping everyone's HP at full, while experienced healers know how to DPS while making sure everyone stays alive. There are a few instances towards the endgame where you do need to keep everyone topped off, but in low level dungeons it is most of the time unnecessary. The out-of-combat regen is insanely high, you get faster Limit Break bars from healing people at low HP, and most of the time, a healer who is willing to DPS leads to shorter fights and faster dungeon runs.