One of the largest weaknesses I have seen in this game from the begining is that the very first set basically set health totals in stone, unless UDE was to do something drastic, phasing out all the older heroes.
The way I see it, the game orignally was designed to make mages a more "control" type calls, with cards like counterspell, frost nova, and card advantage. It was further enhanced by adding in cards like slow, fizzle, and nether fracture.
Now-a-days most good control style decks seem to be warlock, priest and warrior. They have alot of good control style cards, and in the case of warlock and priest, they have access to the same equipment mage does.
Even for fast direct damage type decks, mage falls short. The instant burn available is not all that great, the slower burn doesn't seem to be that great either. To me, right now, the master of burn is the shaman, possibly the druid.
This leaves mage with card advantage and "tricks". They have alot of ways to draw cards and cards like ice block, cold front, and dragons breath to keep themselves around long enough to be a bother.
With this in mind I do not think that mage is a very viable class to play competivly. On a local level, it can work great, if you already know what your going to be coming up against, mage can play a "reactive" game, waiting for the bombs or winning via card advantage. You will know whats in your opponents deck most of the time and can play accordingly. At a higher level, I feel you are relying on luck to pull out wins.
I do not think UDE can really start making mages with better flips, or errata the old cards to fix the issue. That will simply make certain talent specs and older heroes not worth playing. Unless they simply put 4-6 mage heroes in the next set all with good flips. However, mage flips need to be brought into line with the rest of the classes. To me they seem to either all be overcosted or only marginally useful.
Without changing health or flips to "fix" things I think that mage needs to have some powerful mage only equipment or mage abilities that can help them carve a niche into the meta for this game. In all honesty there should be some reason to sacrifice 2-3 health. Access to powerful equipment and abilities could be the answer.