Fedora isn’t that secure without some effort either.
Fedora’s philosophy is being a modern and security oriented (not security focused) distro. An easy example is that Fedora uses Linux kernel 6.14.2, whereas Debian uses Linux kernel 6.1 (I know they backport fixes, but the point remains).
Unfortunately, I have no way to confirm which one out of them is “more secure”.
Do you have any sort of automated test framework in mind which one can use to test distros against attacks?
Generally trust what security experts say about it, but if you really want an automated test, you can look at Lynis
For the same reasons KeePassXC encrypt their databases and Signal got backlash for storing encryption keys in plaintext. Encryption doesn’t protect against everything, but it is a big deterrent against many attacks.