But, the stats WERE downgraded. My player who had about 78% across all stats now has 60% across all stats.
As mentioned, these are not their stats. % only shows the relative value in your current level, like stars. The player real skills and attributes can be checked on his profile, and you will see the real values, like Creativity 89, etc.
You mean the "Skills" tab? It shows % too, only totals for Defense/Attack/Physical are seen in real values.
Yes, and this is a relative value, but you can also check his real absolute value for each skill. This value never goes down even if you promote, only the number of stars and % changes, as every higher level has higher requirements to achieve 5 stars and a specific %.