Ideas and suggestions.

Surely, no one is surprised that stone golems turn into iron golems, or that Serpent's Flight turns into Dragon's Flight. After all, "upgrade" is just an in-game term. Imagine it's not a transformation, but an exchange. Maybe the hero behind the scenes is negotiating with the leaders of other clans: "I'll give you goblins for wolves, and you give me orcs for boars." I don't see anything wrong with that.

Okay, I might have been too categorical about Crag; it's just my personal opinion. Yes, I believe that in a free pick, Crag is currently the best choice for Stronghold on most maps. Zhubarkass, Dessa, and Gurnisson can be better in certain situations. But there's a rule that the easier a hero is to start with, the weaker they are in the long run. And that would be fine, but there are starts where Stronghold is just bad, for example, if you get a lot of low-level ranged guards, like a Master Gremlin, and you can't give away wolves. And that's where a hero with Boars would fill a niche: in the long run, they're not that useful, but they always have a stable start; the boars will tank, and it's not a big loss to give them away little by little, while the goblins will do the damage.