Eddie Murphy is a wonder voice actor

I despise the Donkey character, but his role in Mulan as Mu-Shu was pretty good.

Celeb casting in animation is a touchy subject because the producers often want the novelty draw of the celebrity to sell tickets. That said, voice acting is acting.

There's probably two dozen working animation voice actors that could've done the Donkey role and I would've loved it. Those actors don't necessarily have name recognition like the top line celeb billing, but they can act circles around the more recognizable names.