Hmmm...I don't know if I'd agree. Over all, I find Olivier to be quite crisp and bold in his Shakespeare films. in Henry V, he is incredibly heroic (though rather one-dimensional), and the film is marvelous in color and the Globe "framing device" is terribly clever and inventive. The comedic "wooing" scene is the one moment where he opens up and displays more of the human elements of the character, and it is as charming a version of the scene as I've ever seen. I far prefer his booming versions of "Once more unto the breach" and the Crispin's Day speech to Branagh's (though Branagh's Crispin's day speech had great music to underscore it).
In Hamlet, he is very princely, aristocratic, and eloquent, but a bit too heroic. It's not a great reading of the play, but a great film in its own right. I love the castle and its labyrinths, Walton's great score, and the death procession at the end.
Richard III is a somewhat stagey film, but Olivier is near definitive, IMO as Richard, and he surrounded himself with a large cast of great actors, particularly Ralph Richardson, in a rather unorthadox, and sly performance as Buckingham.
Othello is little more than a film of John Dexter's production of Olivier's stage performance as Othello, but again, I find Oliver to be definitive in the part. He seems to be the right age, has a basso profundo voice much of the time, and the breakdown from smooth eloquence to what Meisel (in the commentary to Welles' Othello) calls "fractured syntax" is perfectly realized. In the scene after he's killed Desdemona, and realizes his error, i felt I was watching the authentic ravings of a real man who has made a horrible mistake. He picks ip many aspects of the part that are missed. If Welles emphasized Iago's impotence, Olivier emphasizes his Othello's sexual charisma. If the Venetians think less of Othello for his race and religion, Olivier's Othello seems to feel superior to all of them.
I agree with your assessment of the sort of absent-minded portrayal Olivier offered in Rebecca. I have never cared for his performance in that film. Indeed, I do not much like the film, which I find devoid of any suspense. I suppose it is interesting as a gothic romance, but is is very poor Hitchcok, IMO.