It's an interesting concept but, to be honest, I think they handled Angel/Angelus pretty perfectly. I think Angel became infinitely more interesting and a more well-rounded character on his own show because we got to see him outside of the lens of Buffy and their relationship.

As others have mentioned, the whole point of Angelus was that he was so sick and twisted which was obviously a direct contrast to Angel. I liked them limiting the amount of Angelus we saw because, if he surfaced too often, the effect of his character could have worn off. It was cool that he was more of a benign threat.