I have 2 questions about the need of the delta:
1) As the "move_and_slide" function already apply the delta to the velocity. What is the interest to apply the delta to the gravity (who will only affect the velocity)?
2) Even without the 1, the physic_process has a fixed delta, is-it not useless to multiply the gravity by a fixed value?
Yes. Formatting is lost on questions posted as well.