What angle do you have with the MAX 9? The fleet isn't grounded or anything. I'd suggest stressing that you had a connection involuntarily added to your itinerary. That should be enough to at least get you back onto a XXX-SFO nonstop, and if that doesn't exist or isn't at a conducive time (which sounds like the case), then the nonstop FRA-SFO. The service quality provided by frontline agents, even in very obvious scenarios such as yours, has gone downhill in recent years.