Free Cities with late game tech?

I just got absolutely destroyed attacking a Free City around Turn 20 when it cast Meteor Shower on my attacking army. That's a Tier IV spell, 80 casting points. Along with the other spells it was casting every turn, the Free City must have had far more than 100 casting points.

Am I missing something? I've played a fair amount of the game, and attacking Free Cities early on in the past was a fairly straightforward option.

But if Free Cities have weird high level tech that unlocks spells that can obliterate early game armies, that really changes the game, a lot. That means that diplomacy is pretty much the only option until you can build up overwhelming force.

I don't think they should be pushovers, but turning them into the equivalent of a Gold level landmark type fight really limits options, which doesn't feel great. It also makes for a really nasty surprise for players who haven't encountered it before.