At the Artios Awards in 2013, "Family Ties" star Michael J. Fox revealed that Matthew Broderick was almost cast as Alex P. Keaton — and the two actors often found themselves competing for other roles, as well.

“He’d usually go in first for auditions, and you’d hear hands shaking,” Fox said. “I was always losing jobs to Matthew Broderick.” But Broderick was unavailable and Fox went on to score the role (and three Emmys!).

https://tvline.com/lists/tv-actors-almost-played-different-roles/matthew-broderick-family-ties/

That's what I read too. Broderick is a good actor and he IS Ferris Bueller, no one else could olay Ferris; but honestly, Michael J. Fox really brought a lot of energy to his character and to the show. I doubt Family Ties would have been ad successful if Broderick played Alex Keaton.