I found this video about a pro artist that uses the gradient map technique ( https://youtu.be/3Zkh8KV2vbQ )

Of course I HAD to try it on Krita and have been doing experiments.

Advantages:

1. Fast for making color changes
2. Easy to see if the drawing looks tridimentional on grayscale

Disadvantages:

1. Heavy on memory use
2. Any extra modification has to be done on other layer.

It was interesting... but exhausting. I'm using the technique for drawing made by hand, the look is better than "overlay" or "multiply", I'll revert to my usual technique for other things.