A nice reading about if your lens (glass) is sharp, or is it anything else?
Article at dpreview by Roger Cicala (lensrentals.com)
Long story short, it is not only glass that makes your lens sharp. It is also the body of the lens, the precision of engineering of lens and also body; also (auto) focus errors, calibration issues. This also goes for the pricier part of the lens selection.
Once I used to try out used "old built like a tank" Nikkor lens. I thought the less used the lens the better the picture. Guess what? The major logic was, the more worn the lens, the better the picture. I was even able to find Nikkor 50mm 1:1.4AI lens with the edges of diaphragm so worn out that I was thinking I was sent broken lens. The reality was, the lens was that sharp and contrasty that the users through all time had understood it well and therefore the lens was also used a lot. I'm using the same lens today and it still outperforms any current and past 50mm primes, including the ones with premium price.
A nice though at the end of the article: "Trying to find exactly the sharpest copy of the sharpest lens is a fool’s errand: you’ll be looking for something that doesn’t exist"
Of course the sharpest copy actually exists, it is just that you don't have the time and possibilities to find it, nor there is any reasonable reason to do it; and it is also true that the perfect engineering just does not exist (with given budget).