I think that, instead of comparing the two numbers and saying "this
number is 25% greater so it should have 75% odds to win against the
other", we should compare skill levels by comparing how difficult it
is to achieve one from the other.
The example was 10 and 15. How many sessions do you need to achieve a
rank of 15 from 10? You can do it in the inmense number of two
sessions. If you just increase the skill once per session, it's five
sessions. Does it make sense that you can beat the pulp out of your
former self from five sessions ago?
IMHO, no.
Greetings,
-Sergi Díaz