Have you tried disabling the Barbarian faction in the editor? ;)

In general, before balancing the Barbarians, you need to learn how to play as them. For example, Seaman considered the Barbarians to be quite strong on Iron difficulty. Chameleon, Mordount, and Gagatek performed amazing feats with the Barbarians on the Circle of Magi map. Also, they are quite good on the PS (presumably referring to a specific map or game mode).

This isn't about me, by the way. I play Barbarians rather poorly.

You can disable anything:) But that's not interesting:) If disabling skills or spells can still provide some benefit, then disabling factions is a different story! Otherwise, you can end up with only advantageous factions on the map. And that's not necessarily wrong, but it's just not interesting... it reduces the choice of tactics and interesting solutions...
I completely agree that you need to be able to play a specific faction. But sometimes, on a map, you know in advance that playing with a certain faction is, if not impossible, then very difficult without a certain amount of luck and a specific set of circumstances. So, what's the point of disabling it? Wouldn't it be easier to bring everything into balance? For the Barbarians, for example, you could add a Conservatory, to level the playing field a bit :) After all, it's very difficult for Barbarians to learn magic... they are fighters! And this would be at least some kind of solution :) Go to a hut - learn magic, or eat an altar, run around the shrines, and then you can also go to the Conservatory: buy magic for the future. Well, that's just my humble opinion :)