Knots are also handy for navigation as 1 nautical mile equals 1 minute of latitude. And of course a knot is 1 nautical mile per hour. So if you're doing 300 knots, that's 5 degrees of latitude per hour.
The units fit together nicely as a system.
"1 knot is about 100 ft/min which is very convenient for descent at a specific glide slope (i.e. for 100 knots ground speed at 5% slope you want 500 ft/min descent rate). Standard is 3° which is about 5%."
You are right. It's an easy calculation. But I would say its easy because its historically based on imperial units. Its easy to think about easy calculations like this in metric units like:
A 5% slope means descending 1 meter vertically for every 20 meters horizontally.
Glide slope of 3.6% would fit nicely though. Then, 100 km/h ground speed goes with vertical speed 1 m/s.
Metric navigation would use the fact 90 degrees of latitude is 10,000 km.
Another example: The feet is cleanly divisible in thirds, quarters, and twelfths, which is greatly appreciated in industry and particularly construction.
Also to be bluntly mundane, almost everyone can just look down and have a rough measure of a foot which is good enough for daily use.
Also, the "sterility" of metric doesn't do it any sentimental favours. Japan loves measuring size/volume in Tokyo Domes, for example.
Jokes(...?) aside though, your absolute deference to precision is an example of why metric flies over people's heads. Feets, Tokyo Domes, arguably even nautical miles and so on are relatable at a human level unlike metric which is too nice and clean.
EDIT: numbers in those languages are the same way as in English, the "ones" are at the right. Kinda strange!
If you can see a 1x1m tile from the cockpit, you're dead.