Title is quite self-explanatory, reason I wonder is because every now and then I think to myself “maybe distro X is good, maybe I should try it at some point”, but then I think a bit more and realise it kind of doesn’t make a difference - the only thing I feel kinda matters is rolling vs non-rolling release patterns.
My guiding principles when choosing distro are that I run arch on my desktop because it’s what I’m used to (and AUR is nice to have), and Debian on servers because some people said it’s good and I the non-rolling release gives me peace of mind that I don’t have to update very often. But I could switch both of these out and I really don’t think it would make a difference at all.
Some answers to your first question you can find here: https://madaidans-insecurities.github.io/guides/linux-hardening.html
For the second question about in what ways Secureblue do mitigate that you can find more here: https://secureblue.dev/features
The last question about usability, is very usable. If you use Bazzite you may have a similar experience. It is not like QubesOS that isolate all processes making it even not able to use a GPU.