I can't say I've noticed managers ruining a team's future and then leaving the team and picking up a different one. I've missed that and wonder how much it really happens - if it happens.

My main disagreement with you though is on the difficulty of maintaining a team at the top. I think once you get a truly solid top team in a league it is VERY easy to stay strong. The fringe players may have short careers but guys like Clemens, Bonds, A-Rod, Pujols will be solid for 10 years or better. Once you have a lineup with Guerrero, A-Rod, Pujols in it and Pedro Martinez, Jason Shmidt, and Johan Santana with perhaps Joe Nathan in relief; you are going to fight for the division lead every year or walk away with it even if you don't draft well or make good trades (assuming you don't trade your core).

What happens next is the other managers in your division get discouraged and leave and you find yourself facing a different set of managers each year or several unmanaged teams. Not too tough to outmatch that competition.

The teams that cycle like you suggest are very likely teams without that strong core but see a chance at a shot at the title and go for it THIS year realizing they may sacrifice a chance for a mediocre season next year. Managing those teams is a challenge - when do you go for it and when do you concentrate on building.

Strong teams are like encumbent politicians. They don't have to work very hard to stay on top.