Equivalence Principle

Why inertial and gravitational mass is always equal?

Assume Newton's second law (F=m*a) is true.
Assume we used a weighing scale to measure the gravitational mass of an object on the surface of Earth. A weighing scale actually measures force. But since we know (free fall) acceleration is the same for all objects on the surface of Earth, we can calculate gravitational mass of the object as:
m=F/a

Now imagine a thought experiment:

What if gravity of Earth instantly switched to anti-gravity (but with same magnitude as before)?
Then the object would start accelerating away from Earth. What if we try to calculate inertial mass of the object by measuring its acceleration? Realize the magnitude of that acceleration would be still the same for all objects, but with reverse sign, since direction of acceleration is reversed. Then we have:
m=(-F)/(-a)=F/a

We assumed that magnitude of gravitational acceleration is the same for all objects. Because a=F/m and F=G*M*m/d^2 then a=G*M/d^2 for all objects on the surface of Earth (M: Earth mass; m: Object mass).

So Newton's second law, combined with Newton's Law of Gravity, lead to inertial and gravitational mass always being equal. Then to prove Equivalence Principle, we would need to prove Newton's laws first.

Newton's Law of Gravity (F=G*M*m/d^2) works the same way as Coulomb's Law (F=k*Q*q/d^2) which describes static electric force which is a Quantum Force. Isn't that mean Newton's Law of Gravity can be explained with Quantum Mechanics, or at least it is compatible with QM?

Newton's second law can be explained with QM?

https://en.wikipedia.org/wiki/Equivalence_principle
https://en.wikipedia.org/wiki/Mass#Inertial_vs._gravitational_mass
https://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation

https://en.wikipedia.org/wiki/Coulomb's_law