I'm pretty sure that Muhammad Ali wouldn't have lost to his old sparring partner.

Beating the likes of Marvis Frazier, Zanon and David Bey doesn't qualify you to be able to outbox 'The Greatest'.
Holmes looked great against a sad motley crew of underachieving and average Heavyweights while Muhammad Ali ruled the 'Golden' era of Heavyweight boxing.
Larry didn't have the power to trouble a prime Ali and his skills were inferior.

Ali toys, out jabs and outboxes Larry to a clear points victory.