I am sorry this is not correct and you are massively confounding things ...
Lens systems have in the physical realm clearly measurable contrast and this is usually tested / measured in contrast of line pairs per mm. This can be measured by very specialized equipment which lens manufacturers have (and before that calculated in lens design software which will always have a higher theoretical output than the real prototypes). Imatest produced chrome on glass targets for example for this purpose of measuring line pairs (
https://www.imatest.com/docs/sharpness/).
When one states that a certain lens system resolves a certain amount of megapixels there is always an underlying sensor size which is implicitly thought about. Because: pixels (ie max. line pairs) * sensor dimensions equal megapixels.
In the case of S lenses it is the sensor area of the S sensor. So what you then do when designing a lens is that you define a certain amount of resolution the sensor (the "camera") might maximally have in the future, eg 100 megapixels from the perspective of the year 2009. Of course lens design has other parameters like in reality most importantly the achievable market price, dimensions (which is why we don't have a Noctilux 90 for example), requirements around materiality, sealing, focus system, etc.
This implies a certain pixel size given you know the size of the S sensor which then implies a maximum of line pairs per mm you could record given the amount of pixels vertically and horizontally. In 35mm for example the SL's target pixel pitch of a 100 megapixels in terms of target sensor resolution equates to a pitch of 2.9μ m. The resulting Nyquist frequency is 172lp/mm and if you look at the MTF chart of SL 2.0 35 APO you will see that it reaches c. 50% MTF tangentially with c.74lp/mm.
Optical systems increased in measurable contrast significantly over the years - the 138mm Rodenstock has much higher resolution (contrast) compared to a lens 20 years ago. Or the SK35 XL vs. the 38 XL for that matter.
So the S lenses were designed to resolve with enough contrast c. 50% MTF across the S frame in view of a 100 megapixel sensor ... so what you don't get is that the megapixels refer to a relative size of a sensor size for which a lens system is designed for.
Regarding the quote above - this is something else. He is just talking about the theoretical system MTF and how the relationship between lens and camera MTF is; the reality is that lens designs can be designed to resolve higher LP / mm (which you can plot in terms of contrast via the MTF plot) - it just takes more (larger) lens elements, different types of glass, coatigns, higher tolerances, etc. to achieve higher LP / mm and depending on the reference sensor size you can then easily express the lens system's resolution in terms of megapixels for that capture device as long as you know its dimensions. You also need to understand that there is an element of a definition whereby you say that a certain threshold of contrast, e.g. 50%, is required for one to say that the lens resolves "sharply" a
certain amount of line pairs on an MTF plot.
What this means is that if you take any lens and use it on increasingly higher megapixel sensors (theoretically) you will see that if the scene is detailed enough (ie not a white wall, but sth contrasty like very fine line patterns on white) that at one point the contrast between the lines and the white will decrease below a threshold where we would consider the lens not resolving the details enough anymore or being "unsharp*. The newest lenses can resolve to a much higher standard than older lenses. You can express this threshold as megapixels in reference to a capture device size (35mm, 54x40mm, etc.).
The statement that the Leica S lenses resolve c.100 megapixels comes directly from Mr. Karbe with whom I discussed this. And the Leica optics team has been quoted on occasions to say that the APO SL lenses resolve 100 megapixels up to the edges and even more at the centre ... ie on a smaller sensor that the S! In that regard the APO SL line is unmatched to my knowledge in 35mm consumer lens land. An APO SL 50 will stay sharp even with a 150 megapixel sensor in the middle and up to a 100 megapixel to the edges according to the published MTF plots. Which is nothing short of astounding IMHO.
Best
Paul
It's a very common misconception that lenses have some level of "megapixel resolution". They don't. Lens design is concerned with what's in
front of the lens and resolving as much
subject detail as possible — along with many other design parameters like speed, size, weight, cost, and a host of aberrations to control, etc.
Roger Cicala of Lensrentals wrote about this in pretty easy to understand terms in an appendix to an article. I'm lazy and he's a better writer, so I'll just quote some of it and link the article. The relevant portion is at the bottom of the linked article...
https://www.lensrentals.com/blog/2019/10/more-ultra-high-resolution-mtf-experiments
"I get asked several times a week if this lens or that is ‘capable of resolving’ this number of megapixels. Some people seem to think a lens should be ‘certified’ for a certain number of pixels or something. That’s not how it works. That’s not how any of it works.
Lots of people think that will be ‘whichever is less of the camera and lens.’ For example, my camera can resolve 61 megapixels, but my lens can only resolve 30 megapixels, so all I can see is 30 megapixels.
That’s not how it works. How it does work is very simple math: System MTF = Camera MTF x Lens MTF. MTF maxes at 1.0 because 1.0 is perfect. So let’s say my camera MTF is 0.7, and my lens MTF is 0.7, then my system MTF is 0.49 (Lens MTF x Camera MTF). This is actually a pretty reasonable system.
Now, let’s say I get a much better camera with much higher resolution; the camera MTF is 0.9. The system MTF with the same lens also increases: 0.7 X 0.9 = 0.63. On the other hand, I could do the same thing if I bought a much better lens and kept it on the same camera. The camera basically never ‘out resolves the lens.’
If you have a reasonably good lens and/or a reasonably good camera, upgrading either one upgrades your images. If you ask something like ‘is my camera going to out resolve this lens’ you sound silly."
