It's not an improvement over common closed source Android varieties either, and will certainly have worse app compatibility than Android. Hardware switches are irrelevant if you can't trust the software.
Anyway, it's as secure as any Linux distro as it uses the same standard stack as servers and desktops and does sandboxing[1], which is also really nice from a development perspective. You can harden it like you would a Linux box using standard Linux tools + kernel features.
[1] https://en.wikipedia.org/wiki/Sailfish_OS#Software_architect...
Also, what's up with all the sour grapes from people who use or develop GrapheneOS? There seems to be a general force dismissing Sailfish as insecure, without ever explaning how. Can't we just be friends in a de-googled world? Are people from Graphene feeling insecure about Sailfish as competition? It feels to me like infighting in small churches. It turns me off from ever considering GrapheneOS before I even looked into it.
Well, Motorola is already doing that :)
I for one is happy that there is at least someone out there not happy with the status quo and go with something completely different and homegrown instead of just going with customizing Android and calling it a day.