Although I agree with you, Enzo, that Fredo no longer posed a danger, I don't consider Pacino's opinion any more valid than anyone else's, unless during the filming, John Cazale was instructed by FFC, as part of his "motivation", to portray Fredo's anger as that of a man who still hated his brother and still wanted to get even, and that his later docility while living at the Tahoe estate was deliberate, and designed to throw Michael off the track while he (Fredo) still contemplated and/or planned his revenge, and Pacino was aware of this.

Short of that, this is nothing more than pure speculation on everyone's part.

The only opinions I'd possibly consider more valid than someone else's are those of the authors.