As it is, they're both way too easy to make, there's a definite imbalance. The rarity of the herbs needs to be addressed, at the moment it's ridiculously simple to make these.
Greater Restoration is just plain overpowered, and redundant, anyway. At the moment it's almost easier to make than Heal. It's not adding any benefit by being in the module, so it's probably best it was removed.
I think moving Lurid Mildew to Sithicus dungeons is a great solution; having some sort of rewarding herb there just seems sensible, and this one fits the bill. One possible Lurid Mildew spawn in the back of Veidrava or the Barrow isn't going to break anything, it'll still be far, far easier to get those five hearts. Anyone who's trying to farm from Sithicus, over elite vampires, will be doing it plain wrong, and really just going to be wasting their time, playing alone for hours, wasting god knows whatever consumables and gold in ferry fees, in the most deadly part of the module.
Whether or not Heal potions, in general, should be removed is a separate point. If you look at the state of the module over the last six months before Heal potions went in, I think we can all agree there were no instances of Athina's Curatives wildly imbalancing anything. I've seen literally one used in my entire time here, although I've admittedly not seen a lot of PvP. My first reaction was similarly extreme, but the boogeyman exploiters don't seem to have broken them yet, so I don't think there's a real reason to react.