I created a 32bit float image, and a long gradient on it.
Than i changed the gamma in LUT, and banding did not changed (like 5px/band).
     (if my 8 bit monitor would have been the bottle neck, the gradients would have moved)
So I tested with the color picker, and every 5px had the same float value.
My conclusion is that krita makes gradient in 8 bit and converts it to the desired color space.

Reproducible: Always

Steps to Reproduce:
1. Create long gradient (longer than 256 pixel) in 16 or 32 bit color space
2. Sample the color and watch the values

Actual Results:  
Every n neighbor pixel has the same value.

Expected Results:  
Every pixel has a different value.