It is what it is. You can't solve the problem.
You either get MTFs from an optical bench - which are cross comparable within a specific lens format (not cross format) but which ignore sensor effects - or you get data obtained via a camera-lens system and you can forget cross-comparison but have an idea about the real world outcome (depending on how you do it).
With enough experience, you can compare the results to some degree. But yes, most people can't.
In the end it comes back to the point that I continue to stress - take a bunch of (serious) reviews and take from them whatever you feel is important to you. No review site is the single source of wisdom. Those who state they are, are also the first ones to ignore.