they aren't that similar in mechanics when you really get into it
arpgs (a la diablo) tend to have faster combat and throw enemies at you
mobas (overhead) have their origins in RTS games, so movement is less important and combat speed is slower.
Diablo - many skills, take what you want, build your character, master using the skills at a high frequency against a massive amount of enemies
MOBA - select amount of skills for each character that you tend to use at a slower pace dictated by situation
