People loathe Apple for locking down their own access to their computer, not for security measures. Signed app distribution solves an entirely separate problem- making sure you get the app unmodified. This is a problem with sandboxing. Apple also does have sandboxing, but mostly that’s not what people complain about.

You can have signed apps and sandboxing without Apple being the sole arbiter of what you install. For example, Linux has multiple options available to solve this. Signed repos combined with SELinux, or flatpak, and snap all solve the same problem.