Sure, in pure component count AOSP might be more open, but it’s about as misguided as thinking the clone-a-chrome browsers are helping temper the Chrome monopoly. And honestly, most people will be running GMS and using Play store anyway.
AOSP is still beholden to what google want the Android experience to be, and at least from what i have seen it’s not like outsiders are allowed, let alone encouraged, to contribute.
SFOS has strong GUI guidelines and a specific toolkit/paradigm/… (which when it started was miles ahead of the competition). But that’s about that… it really is a fairly standard Linux distro in most other aspects. (And i don’t say this to downplay the fairly substantial amount of middleware maintained by Jolla that the other mobile Linux distros benefit from, rather that it is part of what it means to be a Linux distro)
And the real selling point, as i keep taking for granted:
There are no ads, no sell-your-soul EULAs, no apps abusing notifications, no apps asking for fishy permissions. Just peace and quiet; everything is just fundamentally uninterested in your personal data, or advertising to you.
And as developer, i still think running Java (now Kotlin) on a portable device is really quite stupid. Apps here start at 100K or so, and that’s like half icons anyway.