@noobcakethanks a lot for your analysis and detailed post
Could you let us know what league setup you used for this test? This kind of drop-off would usually indicate a decent proportion of the players playing in inactive leagues. Some decrease in inactive nations can be expected, as the higher CA players are prioritised for inclusion at game start, and we don't boost newgens to keep this constant as it would be too easy to pick up high quality youth players.
Internally, we're seeing CA rates remain very stable at Active clubs - and as has been mentioned above in thread, other factors beyond progression feed into this, such as AI transfers and team selection.
We're still looking into ways we can balance out the progression rates in inactive leagues, and whilst I'm glad to see more evidence that attribution distribution isn't "broken" anymore, it's still an area we're not fully satisfied with and are looking to improve further.