I find ergonomic keyboards pointless, but I also don't have (or have ever had) wrist problems.
> Compared to my old Acer C312 tablet with a 5-degree angle, typing 90wpm+ for more than an hour is not sustainable.
Who types 90wpm+ when programming? We are programmers, not typists, we spend most of our time thinking and debugging, with only some intermittent spurts of typing activity. For spurts of typing, the Model M is perfect. If you had to write a lot continuously, I'm sure there are better solutions, but even when I'm writing a paper, the thinking/typing ratio is high.
> Could this be a medical condition on my end, or is there a real ergonomic case to be made for the aging Model M? Right now, I don't buy it.
Given that your work sounds more like stenography and not programming, it is probably just that this keyboard is not meant for you.