Is Vanheim generally considered overpowered? Just asking, I dont claim to know.

[PvK]

I don't think so. Valkyries and Vans are strong but killable and expensive to build up (though less so to maintain). Without claiming any experience in multiplayer play, I expect it's just that you've found something somewhat strong and effective, and been given the time to develop a good bit of it, while perhaps your opponent hasn't found or developed anything quite so good yet. But there are plenty of counters out there.

PvK