No, they're not.

Because as entertaining as they are...we quite fully understand the Corleones from viewing the two films in original form, minus those scenes.
Their inclusion in The Godfather Saga is just icing on the cake.

In my opinion the ONE deleted scene which should have remained in The Godfather is when Bonasera is preparing for the meeting Don Corleone has requested. All the while he's wondering what horrible thing they want him to do...only to find Vito wants his 'massacred' son to be as presentable as possible for viewing.

I think it was a stirring contrast to Bonasera's original impression of the family, as depicted in the opening scene of the movie.

Apple