Well, I understand where both sides are coming from.
1. The tank is unfamiliar with pulling big and therefore have no confidence in his ability to survive a big pack. Meaning he'll forget to use CDs, or in a panic, stand in bad and just drop dead.
2. You and the healer know that Snowcloak is basically a "Pull all the things" dungeon.
The first big pack is actually not that bad. Very little AOEs to worry about. It's the second big pack when you get back outside that is annoying as all hell to manage with those all those AOEs + frost debuff. I don't think that tank would be ready for that and probably take a 30min penalty on you anyway.