Just to be clear; I don't necessarily want fighters to be weak or unable to handle melee combat with dragons, demons, and giants. I just don't think they need to mimic spellcasters in wondrous endeavors. A mythic fighter is already strong, can take blows that would kill a lesser man, and fell great beasts. I just don't want them making strength checks to make new rivers.
Or to put it a different way: I don't mind if high-level fighters choke out the Nemean Lion or wrestling Cerebus, but I don't want him taking Atlas's job for the day...
The question I have is if it's actually enough to be balanced against a Wizard?
It probably depends on a lot of factors, even if we eliminate all the campaign-specific ones.
It could very well be enough. In 4E, a Wizard can cast Linked Portal, a Fighter cannot. UNless, of course, the Fighter learns to cast rituals, but let's say he doesn't and the rules even say he can't. Even then, the Wizard can still be balanced, because Linked Portal is very limited and it costs money and time to cast. Even with a more powerful version, say 3E's teleport, it could be fair, if it's not a cheap spell to cast. Teleport in 3E doesn't have any material cost but it could have one in Next. And that may make a significant difference, since now "novaing" some effects is not just something you fix by sleeping it off, you must earn money for these costly spells.
And you can go even a step further - if you don't want a campaign where high level characters must have 50,000 gp, you can describe each of these costly material components as special items. So in a a low-money campaign, a Wizard finds a Teleportation Stone that he can use to cast Teleport with. But he cannot go to the magic item shop nearby and exchange it against 5,000 gold pieces, since there aren't such shops, and even if there are - the best they could do is trade you in for another magic item of similar item. So the characters may have "expensive" items, but they could still be dirt poor, since there is no way to turn a teleportation stone or a raise dead salve into food. And in a campaign where you are okay with 5,000 gold pieces around, you can allow the wizard with teleport to spend that money to either buy (if your campaign also has magic itme shops) or create (if you prefer item creation rules).
I mention only Teleport here, but it could also apply to other spells. Maybe Disintegrate requires a costly component, and has an instant death effect. But there is a same level spell that has no cost that only deals good damage. The latter is more balanced against the fighter, the former less so.
It will also be a concious group decision what kind of spells the wizard gets his components for once it cuts into the party profits, and this may overall give all players a stronger feel that a particular spell was a group effort. And in addition, there isn't really a benefit to play a spellcaster only campaign in a campaign where 15 minute adventuring days are likely, since the party couldn't even afford all the "nova" and "show-stealing" spells for 4-5 characters.
