In short: I don't think the score is a helpful tool to learn about a lens' sharpness. Quite the opposite actually: It can lead to confusion instead of clarifying things.
The sharpness of a lens depends on many factors:
At which f-stop do you measure?
Where in the frame do you look?
At which distance do you measure?
What do you define as sharpness?
Lets have a look at some 100% crops from the FE 2.8/90:
As you see the 2.8/90 is a pretty sharp lens but at f/2.8 it isn't as sharp as at f/4 and the corners are softer than the center. And that is at 24MP. It obviously doesn't make full use of the sensor at any aperture. If I was awarding that lens a sharpness number (which I don't do for good reason) it wouldn't be 100% of the theoretical maximum. But since DxO doesn't really tell us how they cook up the number we don't know how they get to the number.
The there are other factors which have an effect on sharpness:
The camera used
Lenses vary from copy to copy
Postprocessing
Let's have a look at the lensrentals measurements:
In contrast to DxO we know all the relevant factors:
They are taken at f/2.8.
They are taken at infinity.
They just look at the lens.
They are an average of 10 copies and they also tell us that the lens has very strong copy-to-copy variation.
They give information on different "defintions of sharpness" (I am simplifying a lot here). These different definitions can all be very relevant, depending on application. The more you read up on the topic the more complicated it gets.
DxO is very simple: they imply that they can measure the resolution of a lens like that of a sensor where you just need to count pixels. They can't. All they do is
to measure different things (we don't know what they actually measure) and do some calculations with their results (again: we don't know what kind of calculations) to come up with a number they call perceptive Megapixels. They do that because people have bought cameras depending on megapixel numbers for decades.
Buying a camera based on its megapixel count has never been a good idea. Buying a lens based on DxO's MP score is an even worse idea. There are much better tools than DxO.
