Just checked:
At level 1 it tells you, 1 point of Int will give you 15% more damage. At level 8 the information tells you, you will get 2% per point. And you have a damage bonus of 15% with 13 Int. Down from 15% to 2% in 7 Level. So at Level 10 every point of Int will give you close to nothing additional? There are said to be 25 levels at least, but at level 10 stats just start to mater nothing? That can't be intentional, at least I hope? If I turn from +15% with 13 Int to -6% at 23 Int, players will just feel trolled?
Well if the combined power of skill damage and stat bonus/debuff is still relatively increasing to the last levels damage than that signifies I'mprovemt ', I guess. And then, You out this relevant to enemy damage taken proportionally.
If your just pumping one stat, you should notice an increase in percentage of enemy health/armor destroyed using the same attack at each level.