Maybe new owners could be given teams made up of recycled players.
Whenever a team is converted to a bot, send all the old players to a recycling center, and generate a new roster from players randomly selected from the recycling center. Players could either keep their identity and stat history, or perhaps have a new personality (nationality, name, and face) but existing skills.
When a new owner comes along he takes over the existing team including its players. As the overall talent pool increases, this will gradually upgrade the talent level for new teams. This will also mean that initially only the young players distributed through the draft will have reduced potential. And the potential of older players won't matter that much since even if trained they won't be able to reach All Star status.
Some of the older players in recycling center can be retired. And the younger players will gradually phase in the lowered potential.