They would have to really tank hard to have to wait that long to make it work. There's no reason this team can't be good with a year or two if they ever start trying. If guys are just shredding AAA and the major leaguers are horrible, then there would be reasons to consider calling up guys earlier. A) You have to expect a learning curve in the majors, so the earlier that starts the earlier they can get past it. B) Development can stall if guys are hanging around a level they are dominating for months. C) If it becomes painfully obvious that the only reason they are keeping players down is for vesting purposes, it can cause some friction with both those players and potentially others in the organization. You can erode trust for future prospects about how they will be treated. That being said, they'd really have to be destroying everything with a painfully obvious hole on the big club to make me consider giving up those vesting advantages.