To the developers, i personally think that losing 20% on all players when leveling up not so practical,
after very much effort to train all the players everyday and when it comes to the end of season they all gonna loose stars,
and need to redo again and need to invest much resource if we want to keep at least 120% team every start of new season.
and i believe this is one of the most reason somebody is tanking in the league to maintain their players.
and somebody was suffering by the match fixing because someone got super team but only choose opponent they like to beat
So, im suggesting to eliminate this 20% reduction of quality doesn't matter leveling up or not,
but please introduce the player growth feature which the player will stop growing in skill when reach certain age and his skill will slowly decrease in time.
and at this stage all the managers may need to invest some resource to buy new younger player which still can growing to replace this old players, this is more practical.
please consider this