Let me counter.
The only difference between Megaman and Protoman is that Protoman has a shield and a stronger buster. Otherwise, he's just a clone. Oh and he takes more damage... real innovative.
Megaman and Bass. Same thing really, except he can dash and aim in different directions. Huh.
Axl on the other hand, while playing similarly, has a myriad of other weapons he's used, a hover device with gliding wings that CAN be used for flying, if done properly. (Watch the trailer, maybe he can fly now. X can't do that TECHNICALLY) So, multiple different types of guns... maybe he becomes the long range character. Longer range than X. Plus flying. And that isn't even counting in the transformation chip.
I'm reading potential here. Bass and Protoman don't have that much in terms of potential for uniqueness. I'm looking at this from more than a "lol Megaman" perspective. I'm looking at it from a MORPG perspective, tied in with abilities that have been shown from the series. Bass and Protoman haven't shown much in the way of unique abilities. Axl has shown abilities that set him apart from his comrades.
My two cents.