The linkage that failed doesn't look very robust for the size of model. If it is 4 40 rod its strength is in line with the rod not at right angles as it looks like it was being used. My quarter scale Cubs and Aeronca used a similar setup but the elevator actuator was 5/32 and the 90 degree lever was hard brass on each side the ball clevis silver soldered to the wire. Even if soldered correctly it doesn't look robust enough to do the job. Also it looks like a cold solder joint and lack of cleaning the flux afterward contributed to the failure. In the next pictures is that the underside of the stab? It looks like raw unfilled fiberglass cloth not exactly scale is it?
After all the hoopla I was expecting a lot better. Good luck with the maiden.
Dennis