Quite often the biggest error in a mirror's figure is right at the edge. Masking the mirror down to a slightly smaller diameter might improve image quality.
There is an easy way to check.
Cut a disc out out a black plastic or carboard that has an I.D. about 1/4" smaller than the reflective surface of your primary mirror.
Secure the disk to the mirror clips with, say, 2-sided tape, not touching the mirror. The outer edge of the primary mirror will be completely masked off, including the bevel at the edge.
Then, evaluate the star images. Less in the way of 'hairy edges", fewer spikes, generally sharper star images at higher powers? Then it is likely you made a positive change.
If it makes no change at all, and you see the same issues you currently see, AND you have addressed collimation and cooling issues, then the secondary would be the next place to check.
A similar mask might be hard to cut, and it needs to be thinner, covering only the outer 1/16" of the optical surface. If the secondary is in a holder, you can attach the mask to the holder.
If the secondary is glued to its stalk, I wouldn't bother with a mask for the secondary.
Never paint the edges of a mirror unless it is junk and you just want to make it serviceable and you never intend to recoat it.