Dirty_Player
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Right now, there's a pretty good balance among the 3 elements out of 4 – Water, Fire, and Earth are good in any combination, sometimes even all 3 are taken. Therefore, strengthening Earth by adding Town Portal to it, in my opinion, isn't a great idea.
We've already considered copying Damage Dealer into Air... but haven't come to a final conclusion. It will definitely strengthen Air, but Water will still be a priority – preer, dispel, and bless are significantly better than haste. That is, Air will make sense to take only if Water wasn't given, and for individual classes of heroes to whom it is rarely given in principle (like demons).