??? I dunno why, but I beat Axel first time and it wasn't lucky, to me it was incredibly easy. I dunno, I found many hard bosses easy.
*Spoilers* for RR
I found the Riku II fight very easy in RR, as well as the final boss Ansem. Then again I found other bosses difficult, I guess it just depends on your style. Axel was easy, I used lots of Zeros (I use them all the time, I have killed many bosses when they have over a full bar left with only one single Zero card, while the others were broken). Marluxia was definitely more difficult.