So, a whole lot of DM fiat going on here I think...
First, they're using a helm of teleportation, which is fine, but they are basically using a magic item (rare at that) to mimic what your party's wizard (also 12th level I am guessing?) doesn't even have the spell to do and isn't even a high enough level to do it.
One of the issues in this thread would be for the barbarian to do this without the helm. Now, if they Hulked the siege engine and threw it up to hit an airship and take it out, that would be different.
Second, not sure from how you wrote it but you can't teleport a PC with an object, it is
or; you and up to eight creatures OR an object. If the barbarian did, in fact, just send the object, how did the DM determine your placement was optimal enough to do what happened? If the barbarian went with it, how did you survive the fall?
Third, how big is this siege engine? If they are the Large Object variety, how big was the airship? I would think rather small if a large object was enough to explode its cargo of bombs, especially if there were enough bombs to also talk about another airship behind it.
Anyway, I'm not saying what happened wasn't probably cool as sh!t, but for the purpose of the issues brought up in the thread, the narrative really shows what some people don't w