This is just a guess, but maybe the architecture of the programs is significantly different. MyPaint’s GUI sends a whole bunch of “draw here” commands to the brush engine which build up into a command queue. The engine itself decides how many dabs and where to draw them based on these coordinates and the brush settings, and a bunch of things. But basically it has a list of all the x, y points where your stylus was and can just chew on that queue, even if that means “slowly” moving to each point, at least it has every point to work with.
I’m guessing that Krita has the stabilization filtering magic at a higher level, so that the coordinate/commands of where to draw are not necessarily where the cursor has historically been, but rather in relation to the cursor’s current location. So, as you move to the red line and then away from it quickly, the engine is “slowly” targeting the current location and not trying to get to the red line at all even though your cursor was there. Maybe! I barely know how MyPaint works much less Krita, but based on your video that’s my guess.
SO, I guess you’re just stuck here with us and MyPaint!