Seems, that color profiles in Krita do not affect color mixing in gradient.

See the image:
Gradient from blue to orange.
Krita gives same result in both color profiles (Lab and sRGB)
Photoshop gives other color distribution in Lab mode and more saturated in transition.

I think, gradients should use same color mixing rules which are used for brushes.

http://dobrokot.ru/pics/i2016-01-24__00-36-55_270kb.jpg