Is one excused from the fast-invalidating factors if drops of water are scattered or flow from the upper face into the mouth during ablution, and is it obligatory to dry the face to avoid that?

It appears that what you are experiencing is merely a whisper (waswasah). Water entering the mouth—whether from ablution or otherwise—does not invalidate the fast. If some water reaches the throat or stomach unintentionally or forgetfully during rinsing (madmada) in ablution, your fast is valid, and you are not required to make it up. This anxiety does not permit you to abandon ablution or fasting. You should abandon this feeling, for it is from the whispers of Satan.