You need to update your knowledge to the state of the conversation in 2024. I have myself built and used a 11-46T cogset with a medium cage GS derailer (part Shimano Deore RD-M6000-GS, 10-speed) while having no less than 5cm of ground clearance on a 20"(406) wheel.



It works perfectly, shifting smoothly, crisply and quickly across the entire cogset, affording 21-86GI with a 47T chainring. It's actually quite amazing how well it works. I would not hesitate to recommend it.


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Shimano Deore RD-M6000-GS

​​​Now, as for 50T max cog, there are videos on YouTube and on this forum channel which I have shared showing two other Shimano medium-cage RD that can span with a 11-51T cogset with varying success. Those parts are, in addition to the one listed above:

• Shimano SLX RD-M7000-GS, 11-speed
• Shimano XT RD-M8000-GS, 11-speed

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The point here is that you ought not be so categorically dismissive that it could work in the face of practical evidence that it can work.
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Shimano XT RD-M8000-GS rated for 46T max cog


11-46T cogset for the Shimano XT RD-M8000-GS part

Shimano SLX RD-M7000-GS, 11-speed






Finally there is a Microshift medium-cage RD, Reddleman will know which one, that can span at least 48T max cog.
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Incidentally, a short-cage SS derailer like the Shimano Zee RD-M640-SS part can span a 11-42T cogset.


The trick in all instances, short- or medium-cage, is to finesse the chain length.