I can't say I've played it an absolute ton, but it really doesn't feel like this mod is balanced well for vanilla. Playing against it was absolute hell. Playing as it just felt easy. I attribute this primarily to the Spartan infantry. That is, the base Spartan II. It's absurdly powerful and even if you can get through the shields, regenerates its health above half.

I can't vouch one way or the other for the marine's balance, but they seemed reasonable from what I did notice. Nor can I judge the weapon balance.

Even assuming the Spartans were balanced, the creator admits that John is imbalanced. I think that alone is enough to warrant the removal of the 'Vanilla Balanced' tag. So I'd like to request you either remove the tag or balance the mod.

If it were my choice, I would tone down the Spartan II. Removing the non-shield health regeneration might be enough. Besides, there is a unit out there in the core game specifically for healing another's health. Then move the 'hero' Spartans to a separate mod without the Vanilla Balanced tag. But hey, whatever you want to do.