I'm just going based on how common each failure is. AFM, TPS, O2 sensor failing is quite common. Wire harness failure is fairly common. ECU failures do happen but it's not a very common occurrence. BUT, a bad ECU isn't going to make a TPS or AFM fail. So even if the AFM is bad... then you can add that to the existing list.
If you have access to another ECU to try out then by all means do so but a bad AFM is still a bad AFM....
Which O2 sensor did you replace? The Cali spec vehicles have two, one before the cat and one after. They're not the same. Additionally, if you replaced an O2 sensor which had a heater circuit with a generic sensor which doesn't the ECU will throw an error code for the O2 sensor (GTE models do use these and GE don't but I don't know about Cali spec GEs).