Aargh! USB. Also three decimal places. Is it feasible to make all that debugging info go to the web interface too?
You're right, though, that the question is: what changes in the measured values cannot be accounted for with all the other parameters, but can be accounted for with tilt parameters? As long as there's something, they do provide assistance, but if most of their effect is soaked up by endstop offsets and tower position adjustments, then you're stuck with a highly covariant set of parameters. Even if the numerics can be made to behave, manual adjustment is going to be annoying. The worst case is if the effect on the z=0 plane is identical but the effect on print geometry is different; then you need both for accurate printing but you can't measure their effects by probing the bed.