It will be interesting to see how that comes out and whether the adaptive clear leaves a less wobbly wall finish.
I suspect what was happening before was deflection of the machine due to cutting forces, it would be interesting to see & hear the cut.
Well first, do you really need to cut away all that material with the Shapeoko?
Are you creating a flat plate with attached ridge so all that material in the middle really needs to be cut away?
Around the outside it might be faster to run round in a continuous contour cut with stepover as that would be constantly moving not stopping and reversing as the adaptive clear does.
I would probably run an 8-12mm cutter in my spindle and make fast clearing passes at 4-6mm depth depending on how the wood took the cutting and keeping the Shapeoko out of the vibrating wobbly resonant deflection modes, I described how some of these happen a while ago
The upgrade to a spindle is really not about cutting speed though, the Shapeoko is mostly limited by machine rigidity not spindle power.
I would definitely go over the machine and ensure that I had no slack or wobble in the V wheels and that my belt tensions were all in the zone