Microsoft is about as bad as any other proprietary software company. They do some good things for the open source economy, but they also mistreat their users.
I think it’s a mistake to look at the free software movement as being a reaction against Microsoft or Google. It’s against the proprietary software world in general.
For me LineageOS is a good baseline. I don’t have anything against “privacy” OS’s but they’re not really for me. I just use F-Droid to get apps and don’t care about compatibility with proprietary stuff so neither microG nor the GrapheneOS sandboxed Play services are of interest to me. I don’t use GrapheneOS because I don’t have or want a Pixel phone.
LineageOS significantly increases the lifespan of devices it supports and that’s important to me. Planned obsolescence is cancer.
My ideal mobile OS would be something like Mobian (or even better, a GNU Guix based distribution) but it should be noted that AOSP is also a Linux based operating system and thus anything derived from that is a Linux mobile OS.