the question is more how much the lower skill benefits from the current rule if both succeed
I know, but it's a question that sounds important but isn't.
Here's a thought experiment:
First, imagine two players each have a skill of 10. Here's all 400 possible scenarios:
Blue's roll is on the left, Orange is on the top. Blue cell means blue wins, orange cell means orange wins. A win is either because you succeeded and the other failed, or because you both succeeded but you rolled lower.
Now Blue gets an extra point of skill. The whole table remains the same except for the row where Blue rolls exactly 10:
The red cells (and all the orange cells above the red line) are the scenario people are worried about: they both succeed, but Orange (with the lower skill) rolled lower, so orange wins. And, yes, Orange gets 9 new cells where they win with the lower roll even though the other succeeds, whereas previously they each had an equal number, so technically "if both succeed, it is more likely that Orange wins". But notice that if Blue had not gotten an extra point, and Blue had rolled exactly 10 and Orange had rolled 1-9, Orange would have won anyway. So nothing has actually changed.
But then we have the green cells! Those are brand new and different. Those are cells where previously both lost, but now Blue wins the match.
So when Blue gets a new skill point, he has more new ways to win, but Orange does not get any new ways to win.