Something people tend to overlook in this argument is the scope of play in 4th Edition, which assumes characters will go all the way to level 30. Most other editions capped at 20, introducing higher level play as optional rules and variants. More levels means more powers and abilities to fill out those slots with increasing power, scale, and granularity.
Now throw in an expanding list of classes being introduced every year for a new PHB, as originally intended, each with 30 levels worth of unique powers that defined what the class (with 2 subclasses to begin with) does apart from everyone else. And don't forget the other sourcebooks for Martial, Arcane, etc. that expands those subclass choices for each class.
Also, let's not forget heroic themes, paragon paths, and epic destinies, which layered even more powers on top of everything else. And all this comes before Essentials was introduced to rehash old ideas into something different while still trying to be backwards compatible with previous designs and content.
The variation for mechanical effects vs the sheer number of unique powers as intended by design for this edition was part of its own flaw of being short-sighted. A different approach, like reusing similar powers for a class by power source with different options or feats defined by class or race, might have been more efficient and interesting. Or even just scaling back to 20 levels, or even 10, would have allowed a more complete game in a single book with expansions adding new tiers and higher-levels of play for those who can invest in a longer running campaign with more complex combats and magic.
Despite the flaws, I think 4e accomplished a lot just showing the potential that D&D
can be something different and still give you the same core experience of every other incarnation of the game. If you kick down the door, kill the monsters, and level up your characters, it's still D&D.
