I really don’t know how Mickey has become so iconic because he’s frankly quite boring. He has almost no flaws as a character, and he’s the best at anything he tries, especially in the comic books.
Mickey has a very undefined character, you don’t know much about him, except for the fact that he’s… A friendly mouse with friends? While Donald is a down on his luck, scrappy, adventurous Indiana Jones type, if he was a single parent with anger management issues.
Mickey’s supporting characters are: gender swapped himself who loves him unconditionally, Goofy who’s actually a much better character, and a bunch of bad Goofy clones like Horace the horse.
Donald has: the nephews who got better with each iteration (except for the sk8r 90s 2cool4skool phase) , Scrooge - his rich uncle with the deepest and most complex backstory in all of disneydom, Daisy who to be fair is also basically a gender swapped him/romantic interest, but what makes this relationship way more interesting is the fact that they are as dysfunctional as the B12. And that’s not even mentioning the colorful cast of other characters such as Gyro Gearloose and Gladstone Gander that inhabit the extended duck universe.