Mana flags.

[Exodus]

Since you don't have as much mana, as you have hitpoints it's not necessary to add another aura to the factories.

Few years ago there was a mana recovery item and it was imba

That must have been before 8.15. Because I don't know about it.

The Ultimate Pack used to regenerate mana. But it was kinda too much for just one item, so this was removed.

There is absolutely nothing wrong in adding an item/ability which regenerates mana. I don't see how this would promote camping, as you can use this offensivly as well (and you already have mana regen while defending - thanks to all the factories). The only problem I see, is to find an item which is worth adding a mana regeneration bonus. You need mana especially in the end, where you also need every single slot of your inventory. I can't imagine someone sacrificing one item slot (-> fire power) just for more mana regeneration alone.