To state that unconnected yokes (or side-sticks) have no direct relation with this (and with AF447) crash, is to not understand what basic flying is.
In the bus, with unconnected side-sticks, the PM is only able to see aircraft reactions (to the PF inputs), not the actions that led to those reactions, and this fact makes all the difference...
From the (AvHerald) report:
(my highlights at bold)
The NTSC analysed that there initially there had been responses to the upset on the right hand side stick only, later followed by responses on the left side stick and wrote: "The first left side stick input was at 2317:03 UTC for 2 seconds, then 15 seconds later another input for 2 seconds, and at 2317:29 continued in dual input until the end of the recording. The sidestick priority logic, when one pilot operates the sidestick, it will send the control signals to the computers. When both pilots move both sidesticks simultaneously in the same or opposite direction and neither takes priority, the system adds the signals algebraically. When this occurred, the two green Side Stick Priority lights are ON and followed by “DUAL INPUT” voice message activation. If this occurred, the PF or depending on the PIC instruction, should stop provides input on the sidestick or a pilot should stop the „dual input‟ by pressing the priority pushbutton for 40 seconds or more to latch the priority condition. The FDR did not record neither pilots pressed such button for more than 40 seconds. The CVR did not record “DUAL INPUT” voice message as it was supressed by “STALL” voice warning. The FDR recorded at 2317:15 UTC the aircraft pitch reached 24° up. The PIC commanded „pull down...pull down‟ and at 2317:17 UTC the FDR recorded second Stall Warning. Following the command „pull down...pull down‟ the FDR recorded the SIC side stick backward input increased. The aircraft pitch and AOA were increasing. The average of the side stick inputs recorded on the FDR since the A/P and A/THR disengaged until the aircraft encountered the second stall warning indicated that the SIC was pulling almost full back input while the PIC was slightly pushing nose-down. The sum of both side stick inputs commanded nose up pitch. The pitch up input resulted in the AOA reaching a maximum of 48° which was beyond the flight director envelope and the flight director would have been disappeared from the PFD. The pilot would no longer have guidance from the flight director. The pilot training for stall was intended to introduce the indications of approach to stall condition and recover it. While the aircraft system designed to prevent the stall by providing early warning. The pilot training and the aircraft system were intended to avoid stall. The condition of AOA 40° as recorded on the FDR was beyond any airline pilot training competency as they never been trained or experienced. The degraded SIC performance and ambiguous command of the PIC may have decreased the SIC‟s situational awareness. Consequently, the SIC did not react appropriately in this complex emergency situation. This resulted in an aircraft upset from which recovery was beyond the procedures and philosophy of training that was provided to flight crew and the increasing difficulty of aircraft handling as the result of the rudder deflection which provided roll tendency."
In the Amsterdam and S. Francisco cases, no one noticed the developing upset situation. We can not compare, what is not comparable...