First, the ratings only apply to a specific camera body. Certainly not across brands.
People tend to look at the numbers but misunderstand what they mean. They are forever comparing ratings from one brand to another, a 12mp camera rating to a 32mp rating. The DXO ratings cannot be used that way.
Sharpness (Acuity) is far from the only quality of a lens, in fact, most lens reviewers measure contrast (MTF). DXO's score, unfortunately does not tell us a lot about a lens, and it is not a measure of sharpness. Certainly acuity and MTF are factored into their score, but it is incorrect to use the DXO overall number and say that represents sharpness.
What factors in to their rating? - They say:
The DxOMark Score
considers the overall performance of a lens plus its performance when used with a specific camera body.
Do they measure coma
What about Autofocus accuracy or speed
What about IS
Their is a lot of improvement that needs to be done in their ratings, several times they have been called out for totally wrong ratings, and after defending them, they silently updated them to correct them.
I would not put much if any value in their ratings, since they seem to be unreliable, and use undisclosed weightings that often do not seem to match the real world values that other reviewers take into account.