Hmmm. Queen Of Thorns, Rook, TorchBearer, and Regulus all have the ability in one usage to annihilate almost any special Minions you can summon. I don`t believe micromanagement could thwart that. I am skeptical.
Don`t special Minions already give their controller experience for their kills? Not sure...
As for Yetis being on their own versus structures, yes, but lets not forget how reliant & focussed Sedna is on her entourage. If anybody can leave 8 Yeti-like/Yeti-tough creatures on their own for a period of time, its Sedna.
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Counter-proposal: if you bestow experience for the slaying of a Demigod`s special Minions, then reduce the experience bestowed upon the slaying of that General him/her/itself. If the General is on their own, one ought then to benefit less from the slaying, as they are - without posse - less capable. And if they are not less capable bereft of such a posse, then I submit to you the special Minion system is broken. (Though that is not the point of my counter-proposal...)