Not necessarily, there are tons of things that are very secure but not at all private.

But… having a massive attack surface and known security issues and thinking your data is somehow private because you use a FOSS application is silly.

EDIT to answer your edit: partly. I mean regular timely security updates seems to be a struggle for most of these android OS but also because it provides a bunch of privacy by default options that these other android ROMs don’t such as a private relay, default RCS messaging, and makes them easy for users.

Personally I think if you look at what privacy features CalyxOS actually offers or read reviews from someone like kuketz you realize its pretty lacking in both privacy and security.

What Calyx does offer is a decently degoogled experience for people who don’t have the budget, access, or want for a Pixel with GOS.

I understand your issues with Apple, that’s fair. OTOH I think their offerings, such as private relay, RCS messaging by default, properly implemented sandboxing are objectively better privacy features then what most android operating systems can offer. They also are much more reliable in terms of security updates.

I also have had issues with Calyx using pretty obvious lies to market themselves such as saying the OS can’t be tampered without your knowledge. Not that Apple doesn’t have its fair share of blemishes.