Another question about a new season

[ProVeN]

Are stats based and balanced on the current level as well?

Yes, they are.
100% = 6*
80% = 5*
60% = 4*
and so on

These % just mean how well a player is fit to play in your current league compared to the standards.
Your players don't get worse or lose any skill, they just aren't that good anymore compared to the current league.

Just like in real football, if a team is promoted for example from the second league to the first. The players are just as good as before but they face a whole new set of more skilled players and therefore are less worthy.