Your feedbacks really interesting. Whilst the Spindle mount has a small footprint it have very little flex in any direction - when it’s clamped down to a flat surface you have to apply some serious pressure for the mount it’s self to move. Granted you might see some twist on the V wheels you should not see chatter. I myself ran a 2.2kw spindle with 80mm mount with only 2 M5 bolts and got zero chatter - I’m not stating that is ideal, but I do believe the spindle mount provided with a shapeoko is adequate for the dewalt.
If you feel it’s weak I do have a solution mind - I’m offering up a machined 80mm spindle that clamps to the front with M6 bolts. It does mean you need to upgrade your router to a spindle mind
On a more serious note, if your getting chatter on a regular basis something is loose or miss aligned. In some cases the V wheels might be deformed or damaged, even not tight enough. The Chatter can also be caused by a slack Z belt as it doesn’t hold the axis in situ properly, thus when making a cut the router is bouncing.
I have also made adjustments to the V wheel spacing allowing for those V wheels on the X carriage to be tightened more than usual.