I'm pretty new to the game. Yet I've been reading a lot, and I have plenty of experience with mtg and similar ccg games.
For the games of MW i've played (not much, less than 30 probably) and what i've read, I understand the power of wizard and his versatility, yet I think that he's only overpowered on the "pro" game, the casual player, specially offline, doesn't get really hurt by this. I mean specially offline because a lot of people have not all the expansions, so not access to 6 dispels, 6 dissolve, and 6 teleports. Also when they have it a lot of people rather have a few balanced books than 1 overpowered.
So the issue comes to balance the mages at tournament level. And here is where I will start my line of thought.
Dispel, teleport, and dissolve are powerful because they have not inherent counter (as it have been told many times on this post). If the future expansion have enchantments that can't be dispelled, or obscure, conjurations that penalty teleport, equipment that can't be dissolve, or conjurations that penalty dissolve, or any way to make this 3 specific cards less appealing, everyone including wizards will start playing this cards, but this will cause an extra effect, when a card is less effective people also stop playing it, if a wizard see he's finishing most of his games with only 1 or 2 dispel useds and lost because of it he will take out of his spellbook this cards to fill it with counter measures for the new enchantments, conjurations and equipment. New cards if done in the good way can bring balance to the game in the sense that: If everything can be countered, you have to be really careful with how much of each you counter. As people stop playing so much dispels and so much dissolve people will also stop playing their counters, and with enough time the game will achieve (or get close to) balance. But to achieve this balance the future expansions have to address this issue with precaution. As it have been said here too, it would be a shame if the new cards get so powerful that anyone with a brand new game have just obsolete options.
So as I see it, the game can be balanced with expansions that nulify the current power of current cards, without the need of errata. And errata can be used for the purpose of pro gaming, I don't see how the community would get hurt if the next year of tournaments have a wizard with *3 nature, or novice arcane level 1 spells, making teleport epic, or any temporary measure that would not affect new players and would only be an incentive for pro players to explore and re-explore tactics.