Putting your current situation aside, would you find it reasonable if another user got banned from Blahaj from transphobic statements on another community?

Not particularly? I regard bans for off-comm behavior as ridiculous, speaking as a mod. Off-instance behavior seems doubly strange, and I’ve commented on such incidents before.

Furthermore, the issue of whether this is transphobic is, itself, core to to the point - most people would not regard the existence of dragons as a matter that relates to transphobia at all. Yet to Blahaj, it would seem an instance-bannable offense - regardless of whether you’re on their instance at the time of the comment, or even if you ever post on their instance.

Or would you expect the Blahaj admins to wait for that user to make such statements on their communities?

I would expect the Blahaj admins to not be prowling other instances for thoughtcrime.