So one of the many goals that newer versions of D&D have strived for is a “balanced” game. This vague term means many things to different people, but on the whole it usually applies to monsters and heroes engaging in “combat as sport” type conflicts, and the heroes all leveling with roughly equal powers and capabilities. Older versions of D&D were quite unbalanced. Fighters became less useful as level increased, and the puny magic users of low levels became spotlight stealing tactical nukes in later levels. Similarly, while encounters were generally gauged by level, old D&D had no qualms about throwing powerful enemies at weak heroes. Balance is certainly a laudable goal, and certainly allowing all players, regardless of class to enjoy roughly equivalent powers and relevance at all levels is a boon for all, but too much balance can also make a game harder to make your own.
OSR D&D players see don’t see the imbalances of old D&D as a problem, either because they don’t mind, or because they like to replace those unbalanced bits anyway. 4e players on the other hand, reasonably argue that if you have to replace whole swaths of the game to get a balanced game, then the game is fundamentally broken. But there is a pitfall in a heavily balanced game.
Consider the 4e player who dislikes Save or Die effects, or combat as war, or Vancian magic. If you’re playing old D&D, you can rip any one (or all) of these things out of the game, and still be able to play the game, in part because the nothing about the system relies on these things existing. Sure certain spells might be tempered by the fact that they’re fire and done type spells, but for the most part any component can be removed without major effect on the game as a whole.
On the other hand, 4e is a delicate balance of game mathematics. A 4e player who doesn’t like Vancian skills, or doesn’t like the assumptions of magic item availability have much more work to remove these elements and still keep a playable game.
Old D&D is a bit like a fresh jenga tower. Not very big, not very intricate and no so much balanced as it is capable of having parts removed and rearranged while still standing. 4e is more like a late stage jenga tower. Large, intricate and interesting, with each component perfectly balanced on the rest. But like a late stage tower, it also can’t afford to have pieces removed willy nilly.
It’s not wrong to have a balanced game, but if you want a game you can turn into your own, it may be better to start with an unbalanced one.