If the user wants a different root font size, they'll set it themselves.
'Don't resize my fonts' is such a narrow view of whole range of design considerations.
I use somewhat similar formula in one project to create a common baseline font size that 1) does not break with viewport size changes 2) remain legible for baseline user 3) gives good base value to scale UI elements by rem/em units.
Of course it's also a project where the user does not have a chance to mess with font size anyway for the main user, but I'd reuse the formula elsewhere.
Wish I could query the browser if the user has specific preferences, just like with "Dark mode"
Meanwhile using the default size + CSS keyword size modifiers (large/x-large etc.) ended up on breaking on the project I mentioned, especially after for all practical purposes we had to deal with the fact that claims of single display size & resolution to target weren't actually delivered, and when client also asked about possibly opening the interface from portable devices.
Which I suspect is the case for the majority of end users.
You can't query that with dark mode since there is no "no-preference" in the spec and the "preference" that browsers expose normally has not been influenced by the user in anyway. You should still respect the indicated dark mode preference because the user can influence it to set their preference for all sites. Same with the font size.
