@k1tb
I feel you should lose 20% no matter what, at the end of every season.
This will take all the fun out of tanking and I am sure will reduce the tanking teams by a huge number!!!
This will also help in addressing the argument of "what do you gain by progressing to next level".
You unlock higher level players who cannot be bought by a team that tanked.
There has to be some sort of punishment for underperforming and a reduction of quality for your players fits the bill for me