All phones end up reliant on proprietary blobs. Not that I disagree in principle, but we have to be realistic. Hardware manufacturers, telcoms and to some degree regulators all do not like user freedom with regards to phones.
But AOSP is open source while Sailfish OS is not. Also "proprietary blobs" != "proprietary blobs" (there's varying level of obfuscation/debug info).
Isn't the Librem 5 fully open?