It is not clear that hoppers respect stockpiles priority and setting a food pile with critical priority takes the food out of the nutripaste
How do you mean it is not clear?
You can set priorities on both the stockpile and the hopper.
Default stockpile priority is normal.
Default hopper priority is prefered.
So you as a player can set and chance the priorities.
Simply setting your hopper to critical.
And your stockpile to prefered solves the problem.