Surely that wouldn't work if the elevator was jammed up or down much? I would think it would only work if the elevator was jammed almost neutral.
I am sure you are right, because the trim tab is very small.
I think the biggest danger is somebody leaving some object in the airframe, which jams the controls. This has happened; from vague memory a number of times. Control linkages coming off completely (without jamming the controls) are not uncommon too, but they should not cause a crash.
Concorde had an interesting system, whereby strain gauges were placed on the yoke(s) which drove a separate control system so that a totally (locally) jammed yoke would still work - again from vague memory.