Of tangential relevance to the JVs, it's worth pointing out that AS gets a decent amount of business by providing feeder traffic to many foreign carriers that aren't covered by JVs (e.g. BR, CI, JX, EK, TK, ET, QR, OZ, PR, SQ). B6 also fulfills this role, but a bit less prevalently in my observations.

ETA: I forgot about the Chinese carriers that also rely upon AS and B6 to serve the US beyond LAX/JFK (e.g. CA, CZ, HU, MF, MU). Since there are no more slot pairs on offer for them, at present, you could argue that their need for connectivity is much stronger than for airlines domiciled in (more) Open Skies countries.