I can understand why he was cheesed off, but I am very happy that Hulce was cast instead.
And Branagh did end up doing OK for himself.
News reports at the time stated that Tim Curry and Mark Hamill also tested for it. So it seems that at least three of the actors who had played the role onstage tested for it, and I wouldn't be surprised if Peter Firth also tested for it, which would make four if that happened. I suspect Forman was never going to cast any of the actors who had played any of the roles onstage (except in a different role).