He was undoubtedly trying to solve a problem that didnt really exist. Which is bound to create all sorts of difficulties for a person who attempts it...
I'd appreciate it if you didn't pass judgment on the DM without knowing any details. You may love the system, but that doesn't mean it isn't considered irrecoverably broken for some. For example. I was playing a druid, and the DM had effectively nerfed wildshape to make it useless for offensive combat (it didn't pass the ability scores of the animal onto the druid). It was in that "sweet spot" you all love to talk about in level ranges, if I recall, around level 6 or 7.
In every combat, I summoned an animal, buffed it and my animal companion, and then cast maybe a single support spell such as Entangle or Fog Cloud. To look at it from a very generous point of view, I contributed about equally to front-line combat when compared to the fighter, fully decked out in WBL magical gear. I of course had no need for most of that, and spent my gold on metamagic rods, scrolls, and wands. At a rate of only spending 2-3 spells per encounter, I could last around 4 before worrying about running dry, and I think it's the rare adventuring day that goes beyond that. Of course, out of combat my contributions were many times those of the fighter, as I could heal and cure afflictions with my collection of magical items and consumables that the fighter couldn't afford, because he spent his gold on magic items just to compete with my summoned animals on the front-line. Not that he'd be able to use most of those items by RAW anyways. I also naturally had better skill checks, I could scout by using wildshape to turn into small animals... and I had gimped myself somewhat by picking the subpar half-elf as a race. And that is just one example. For more ways in which full casters break the game, I direct you to this link.
The problems do exist in the rules, and the core rules are perhaps the worst offenders of it (try comparing the stats of a level 1 druid's war-trained riding dog companion to that of a level 1 fighter sometime, I believe the fighter only comes out ahead by a very narrow margin). And you might be able to solve them with dozens and dozens of house rules, but why do that when you can design the system from the start without those massive imbalances? If your only defense is "well we can have fun with it," people can have fun playing any system, or without a system altogether. That is not the best sell for the game. We need more than that.
One of DnD Next's stated design goals is to have appeal for everyone. And I am saying that if it wants to appeal to myself and the kinds of people like me, it desperately needs real class balance. It needs to be easy on the DM as well, that means there are limits to how far I'll tolerate needing to fix the problems of the system as the DM (far less than 3rd edition, closer to 4th). I do not feel it is impossible to make the classes different and fun, yet balanced.