heres the thing. the moment he became a playable character next to X, he couldnt be broken anymore for gameplay reasons. in X1 and 2, he wasnt playable, so he could be as broken as the story called for. in X3, he was semi playable, so his 3 shot combo was toned down and the saber wave was done away with and it became a close range saber swing instead. but he was still overpowered, because his sole gameplay purpous is to get through areas that the player sucked at with X's solitary charge shot. he was your crutch to lean on until you got the armor. if youve ever fought a boss as Zero with the Zero code, youll notice that 2 saber swings takes down any boss. in X4 and on, he became fully playable, and they thought of a cheap ingenious way of making him playable, while making him the opposite of X, for game play variation in the two identical segments. they made him close range, as opposed to his previous long to mid range. so they did away with the buster, and focused on the saber. and made him equal to X.
also, you do get to use the moves Zero does in X2. the ground pound is in every X game he's in. Ox simply lets you use all the different ones at once. blocking... that was odd, even for an X game, as Zero is the only character in the X series to ever block like that.