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Would the tiny incremental gain from tweaking one or two specific settings to my perfect liking save me anywhere near the amount of time, happiness, or productivity that I save from just letting someone else choose the defaults for me?There are substantial privacy and security benefits to leaving the macOS/Windows ecosystem. Both of these operating systems include a lot of telemetry that is non-trivial to disable, and both use opaque, proprietary encryption software with a history of catastrophic bugs, including for disk encryption.
The big one though is spyware: Windows makes no farce of it, and is instrumented up the wazoo. You've got to dig into the registry to disable a lot of it, and firewall the rest. Opting out during install is entirely insufficient.
macOS used to be a lot better, but as of Catalina, even with all of the Apple network services disabled, iCloud turned off, Siri and location turned off, analytics opted out, no Facetime, no iMessage, no App Store, et c et c, it still sends all sorts of traffic to Apple, including some to no-hostname 17./8 IPs for some reason.
To get basic privacy on these systems, you have to do hours of work after install, run third party firewalls, and even then you're who-knows-how-many disk encryption 0days away from a stolen laptop meaning total compromise of your data.
This is not to say there aren't any encryption 0days in linux, but there are certainly a lot more eyeballs on the source, for a much longer time.
Conversely, linux doesn't really have anything comparable to Little Snitch or the per-app per-directory permissions of Catalina, sadly.