Why does Morde have such a high base AD...

because he can farm as long as he has high base AD while building whatever he needs.

illaoi has one less base ad and same growth yet her other stats are way better

I agree with the movement speed but his health and armor were reduced for his passive's sake pretty much lol

Melee champions have higher base AD than other champions, and the subgroup which has even more is the group which Mordekaiser belongs to.

You are misunderstanding how the stats work; just because a champion won't be itemizing for them doesn't mean he doesn't need them. They can serve the champion well in that he doesn't need to pay gold for the base stats and can enjoy its benefit. In fact, that can make them more important. As the champion won't be building into that stat, it can be very important for that stat to be strong in its base amounts because it won't be getting better from items purchased.

Everybody in this thread is missing a very valid point.

He has a big fucking mace. Are you gonna tell me that it shouldn't hurt when you get hit by that thing?