“However, around New Years 2022 I ran some various network speed tests for unrelated reasons and noticed that I was consistently getting a speed of ~340/30, instead of the ~650/50 I was expecting.”
An AirPlay button on the Touch Bar kept a background process hunting for devices. That cut the connection to about half its speed and wrecked game streaming for months after a Monterey upgrade. Safe mode didn’t touch it. Apple shipped the fix in macOS 12.5, after the post spread. A user had to do the debugging Apple’s QA skipped.