I'm not going to get into to the "gain wars" (yes, text bok, real-world you can have just one "good" (high gain) antenna, and it will work just fine for send and receive) - but your answer prompts the obvious question: What about lasers? Turns out, before optical lasers there were masers - microwave lasers, bit they were (are?) very limited power:

https://www.scientificamerican.com/article/first-practical-m...

I was assuming geometric optics... because it was simple enough to get the point across. Which of course you knew, but took the liberty to 'correct' anyway. It's quite impressive how you can always count on HN pedants to deliberately go out of their way to technically-correct you while making sure to completely miss the actual point you're trying to make.

You're the one that started in by trying to wrongly "correct" the statement "every improvement in sending is completely equivalent in receiving for a system that uses the same antennas for both directions of communication" (which is actually correct).

The fact that you can't have perfectly collimated beams and must make do with antenna pattern "lobes" is actually important here.