3 sciences with lab is generally the rule (12 credits) + maybe a fluff easy class.
People who pull off semesters like that or work full time + taking full classes and do well are the exception. You see a higher rate of it in these communities because some of the best students in the world are pursuing medicine.
God forbid you get sick a week, or have to visit someone in the hospital, or literally any one of a thousand life conditions come up. There's no small amount of luck also involved in this type of thing, even for super students.
You are planning to mcat on top of it? What are you thinking? If you have to ask us if it's too much, then it's too much.
You are already planning to take a gap year, would advise you to take your gap year prior and use it to spread out your classes and master the MCAT.
To answer your initial question, I would rate 10/10 for both, because I won't entertain putting numbers higher than 10, because once you reach insanity the increasing scale of it doesn't matter 🙂