After reading the paper the effects of leaving it in a high charge state seems to be smallish. The insideevs.com article never says what the size of the effect is, which is a hint it might be a lot of clicky writing about a nothing burger.
In any case if you are the leasing company, you get to control the BMS. The BMS holds the keys to the kingdom. It can control how the battery can be used: charging rates, max charge, how long max charge will be maintained before it self discharges, min charge, allowed operating temperatures. It seems to me they could mostly eliminate the sort of abuse that seems to concern you.
