Past performance is no guarantee. Just because Vancian casting was always broken before, and isn't being implemented in a particularly different fashion this time doesn't mean...
...OK, yeah, it prettymuch does mean it's going to be broken again.
Ultimately, I suppose, this is just a marketing issue. WotC has analyzed the demand for D&D and concluded that they want to sell to people who don't want a version of the game that features any sort of class balance. People who don't want Vancian casters that are wildly overpowered at higher levels just need to find different games - quite possibly games without classes and levels, at all - because D&D is not being made for them. There aren't enough of them, or they don't buy enough books, or they don't make enough noise or whatever: they're not a desireable market.
They made enough noise to give us D&D 4th Edition. It's just this time the pendulum swings the opposite direction.
But we haven't seen high levle spellcaster yet. Maybe they are far more limited then we expect. Currently, my expectation is that it will work as in past editions where a 10th level caster will have access to 4-5 spell levels (I've heard some talk the max level is only level 7?), and has multiple slots per spell level.
But maybe they do something else, and instead, people do not get new spell slots beyond level 3 or 5 or whatever? Instead, some slots just can fit higher level spells. So a endgame caster will only have 12 spells or so, unlike the 36+ a high level 3.x spellcaster was guaranteed. This would make it very hard to bring all the utlity spells to bear, and load up a lot of offensive spells as well.
I am also baffled by this. Also, the wizard may be versatile but is squishy, and can easily die if no fighters are engaging opponents at the forefront. The wizard is dependent on others' defensive and attritional capabilities.
Also, at least in this thread, I feel alienated from the concern about rules that allow "outclassing" or "stepping on each other's toes". This implies that you're upset with your fellow player/PC because they do something that you should be in charge of. I think that's the opposite of interdependency, in which you're watcing each others' backs. It may be a subtle difference but an important one.
In one case, it's a superhero team of alpha males/females teamed together for the sake of convenience and beating the odds. In the other, heroes are humanly imperfectly incomplete parts that complement each other to make an awesome fighting/exploring/socializing machine.
Again the problem is that people do not see interdependence. They see that the Fighter needs the Wizard to do his stuff, but not tha the Wizard needs the fighter for anything. That is where you may disagree, but people have gameplay experience that suggests otherwise.
They have seen people playing min/maxed Wizards that didn't need a Fighter to kill enemies, even against creatures with spell resistance and decent saving throws. They have seen Wizards that could cast Knock to open Locks and used other spells to deal with magical traps. They have seen Fighters die to a random save or death effect that some NPC caster or monster used and the only way to avoid that was if the Cleric had cast the right spell, making him highly dependent on the Cleric. But the same Cleric with that spell and another spell could match the Fighter's offensive combat prowess as well.
But we've also seen all-martial parties in 4E that worked as a team and kill the opposition without needing some spellcaster to save their ass. And we've seen mixed parties where Fighters and Wizards cooperated and coordinated with each other to become more effective then they could be alone.