I know this was endless topic have been discussed before,
i personally think tanking is not a problem, and not leveling up is also not a problem,
but if it bother to somebody who run the league with full effort, this is problem
and this problem will happen only if that tanking team got full of 8*~9* players and may introduce match fixing.
so my suggestion to overcome this problem is to introduce new feature which is;
Any players that exceed 140% (8*) tend to leave the club if:
i) the club not leveling up for next season
ii) that player always put in reserved
and this is true for real superstars, they don't want to keep playing with the club at lower division league,
and a superstar also doesn't like to always warm the bench,
so, if this feature introduced, quite hard for a tanker to keep their super strong team in next season
and others active manager will be not bothered so much to those tanker.
*please note that this is different with token buyers who build the team until become super strong team. this can be consider as their effort, as long as they leveling up, the 140%++ player will not leave the club