It might have been a small factor, but the new strap is definitely much tighter.
With the toe strap on the front position, the right side would skip much less than the left side. With the toe strap moved back, it hasnt changed on the right side (still skips unless i hold the front of the clip), but that is manageable.
The warranty returned strap however, doesnt matter what i do, it just grips and grips. Havent had it slip once yet.
And after a day out on the snow, i can confirm that i am happy with the bindings again. Still not the easiest to put on, due to the curvature of the ankle strap etc (definitely have to sit down to do them), but they are comfy, and have just the right amount of flex for me. Also changed my stance to +15/-15 and no longer have sore knees.
For the boots, i took out the insole of the right side, and used some thin suit socks instead of sports socks, and no more pain there. As that side pads out I can put the insole back in, and then also eventually move to thicker socks.