How long should a successful rebuild take?

Head Coach is more important then any player on the field.
Bum Phillips sometimes joked about a coach being so good that he could take 'his'n and beat your'n and take your'n and beat his'n'. While I won't argue that the truly great teams generally have a few great players to improve the coach's odds of producing a winning squad, like you I do believe that you can't produce a great/winning team without a top notch head coach no matter how good the players are that he's been given.

To me one of the advantages of having a new head coach from outside the organization is that the players must earn their reputation with the new guy who is (generally) not coming into the organization with established friendships or favorites. A totally new guy isn't swayed by emotion. He has a philosophy and he picks the right guys who can best execute his plan of attack.

The one thing that I like about Rizzi is that he seems to want to head coaching job permanently and he may not allow favoritism & friendships to stand in the way of putting the best players that he can find to run his schemes. But it's hard not to allow strong personal bonds have an affect on who gets penciled into the Final 53.