Does this necessarily mean that the two bows I originally introduced as standing options are unstable, not forgiving, and unshootable to such a high degree?
Yes, I would agree. Bows with short brace heights, extreme reflexed risers and very stiff/harsh drawing cams are not forgiving enough for most shooters to shoot accuractely on a regular basis.
The suggestions of the Mathews Switchback or Outback and/or Bowtech's new Allegiance or Patriot single cam would be better options overall. All of them offer slightly more forgiving design characteristics (brace height, riser geometry, draw cycle) without sacrificing much to the other two you mentioned in terms of speed.
If speed turns out not to be as important to you as you may have originally thought then start looking at the Freedom cam bows from Bowtech. The Liberty and Justice are in the mid-range in terms of speed and yet offer a very smooth draw cycle and decent brace heights which make them a pure pleasure to shoot. I would even suggest the Pro 40 Freedom if a slightly longer axle to axle length doesn't bother you.
Hope this helps.