That's more the exception that proves the rule, though. Chrome originally came out when IE was still a steaming pile of garbage, and Google spent lots of marketing money promoting it as a better, faster alternative. (Something that Mozilla had been previously somewhat succeeding at, more or less, but they didn't have the same resources and eventually lost their gains and fell behind.)
These days Chrome just has so much mind-share that it overcomes the defaults on Windows. This is by no means a common outcome. This is anecdotal, but I know far more people who use Safari instead of Chrome on macOS than who use Edge instead of Chrome on Windows; Microsoft just has such a bad reputation when it comes to browsers that Chrome is able to get over that defaults hump on Windows. But a lot of people genuinely like Safari, and trust Apple in general, so the effect is (somewhat) lessened on macOS, even though IIRC Chrome still does have the lead in market share there. Just less of one, percentage-wise.
You're right on some points, other points don't match up with my understanding of the issue.
Chrome was a much better browser compared to the default that came installed on Windows, and certainly if someone is going to switch away from the default they will do it towards a much better alternative, on that we agree.
However, despite how much I think Google as a search engine has declined in quality, I still find them to be significantly superior to the alternatives, such as Bing and even DuckDuckGo (which I believe predominantly makes use of Bing) and that people will switch from whatever default search engine Apple sets to Google.
You're also missing the power of reputation. It takes time to build a good reputation, and it takes a really long time to overcome a bad reputation. MS built itself a really bad reputation, especially with browsers, so even if (hypothetically speaking) Edge were as good as Chrome now, it would still take a very long time to overcome the terrible reputation they earned with IE.
These days Chrome just has so much mind-share that it overcomes the defaults on Windows. This is by no means a common outcome. This is anecdotal, but I know far more people who use Safari instead of Chrome on macOS than who use Edge instead of Chrome on Windows; Microsoft just has such a bad reputation when it comes to browsers that Chrome is able to get over that defaults hump on Windows. But a lot of people genuinely like Safari, and trust Apple in general, so the effect is (somewhat) lessened on macOS, even though IIRC Chrome still does have the lead in market share there. Just less of one, percentage-wise.