This is golden!
The techniche opens your mind to some other possibilities!
I think I improved this a bit!
The problem I was having was that the Shadow is too black so when we have a colored shader(texture applied for example), it wouldn’t reflect the color of shadow for that particular color.
If you stop to think Shadow color is nothing more than a desaturation of a color.
Now look, when we have this Noise Texture the issue becomes more evident when comparing to the Original Shader:
If we change the Black in CellShadingRamp doesn’t work good because it will only change the color of the Black and will not bring “a real shadow color” just becoming the color set to the Ramp…
Then I got the idea to mix, the harsh black with the Original Shader and I like the result!
The shadows get a smoother transition, but it doesn’t really lose the “cartoonish” look:
Made some more improvements to allow some control over shadow and the lit part.
Here’s the file that contains the NodesGroup. Monkey_CellShading.blend (1.1 MB)
How to use:
Append to you file the NodeGroups: CellShading_v2 and CellShading_Ramp
Get any material you have and put the CellShading_v2 on top of the line that goes to the Material Output, play with the Shadow Gamma and Lit Part Gamma values
That’s it…
Some considerations though:
This is for Eevee and will not work with Cycles.
Doesn’t work good with HDRI
You may have to change your material roughness. I found that 0.5 works best for many situations.
Works better with Light Colors because you have better distinction of what is Shadow and what is Lit.
You may need to play with the Scene Lights (specially if you are converting this from Cycles)
Then, decided to try the "Cellshading " node group in the materials of an old project 
(The outline there is freestyle because I would have to add a Solidify to every piece of the car and would take forever)
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Yet another test! 
(Sry having lots of fun with this lol)
This one is actually using the Outline described in 100drips video
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