First, i don't know if it is by design or limitation or a bug, and it is not specific to 2.9.7

I noticed in the smudge engine, there is a hierarchy between Smudge length and Color rate Properties. Color Rate depends on Smudge length, wich makes impossible to make brushes that slightly blend colors while being opaque. Currently it looks like it is possible to use full Color rate, but only with full smudge length. If, for instance i want a "crayon-like" effect, which is opaque and solid, but not hard, it's necessary to allow  a Color rate Value superior to Smudge Length value which would result in an opaque colored stroke that smudges just a bit. But they seem tied together, with smudge length being the master value, and a low smudge length results in a smudging yet transparent stroke.

Would it be possible to untie those two parameters?

Reproducible: Always

Steps to Reproduce:
1.Lower smudge length setting in a smudge brush
2.See how transparent the stroke is.

Actual Results:  
the smudge effects cannot be subtle while being opaque

Expected Results:  
permit 'Color Rate' > 'Smudge Length'