I'm still continuing my research and I had to do a test to stress my new method even more.
My stress test: I had to paint visual effects (fire), night ambiance, fog, a foreground/middleground/background, a perspective system, etc... And because I'm doing all of that in a larger plan to solve many other bottleneck in my production, I decided to go for a theme of "Confront the Dragon". It has an opportunity to study many material at once.
Unfortunately for my test, it failed. I don't get exactly the rendering I wanted. I pushed the artwork anyway so I could post it and the file doesn't sleeps on my disk system.
I wish I had a better way to preserve the silhouette of the ground (foreground/middleground/background/dragon/character) and the layer stack of Krita did not help about that. The alpha inheritance workaround for clipping mask is not fluid to work with, except if you have only one or two group like that in your file.
I'll continue to explore.