But those million win32 applications tend to be really outdated and poor in terms of features compared to the macOS ecosystem. At least that was what I experienced.

Regardless, they're at-least usable and Microsoft cares about backward compat.

Just last week I played a game of Age of Empires II with my cousin, a game which was "released" in 1999 on a Surface with Windows 10. While on my MacBook I have issues because every major OS upgrade breaks something and I have to repurchase newer versions or give up if the dev isn't interested/around anymore.

I agree, Windows is much better at backwards compatibility.

OTOH I've found that it's not such a big deal in practice. In my 10+ years as a mac user I've only hit this problem a couple of times. Likewise in Windows I rarely open old outdated software.

That is of course my anecdotal and personal experience.

It's not a big deal for consumers. It's a huge deal for STEM departments in universities (a software upgrade for a hundred-thousand dollar machine can sometimes be thousands of dollars).