"Quantum action is a bit ambiguous to me."
Quantum action is simply the change in matter over time predicted by the Schrödinger equation, which states that the change or differential of matter in time is proportional to itself. Is that ambiguous?
The proportionality constant is the quotient of the binding energy as equivalent exchange mass associated with the action with the matter scaled Planck constant, h/c2, oh and the phase factor, -i. So the quantum action of matter is somehow 90 deg out of phase with matter itself. If you thought the Planck constant was small, the matter scaled Planck constant is 9e16 smaller still, ~1e-52 or so.
So the Planck scale in matter time is quite naturally very, very tiny. Whether you do action semiclassically or with exchange step operators is simply a matter of convenience. The -i phase factor is, by the Euler identity, simply the same pi/2 or 90 degree phase angle that shows up everywhere and represents the orthogonality of matter and time or Pythagoras.
Charge and spin and gravity are all properties of the same exchange of matter between objects. All objects exchange matter with the universe as an object, which is roughly what gravity force means. Certain objects like electrons and protons just exchange much larger amounts of matter with each other as phase coherent quanta and those large matter exchanges also result in particle spin. The phase of that exchange is what determines attraction or repulsion, which is more of an isospin, i.e., a combined charge and spin.
With a universe composed of such a large, albeit finite, number of very tiny particles, most practical predictions of action need some kind of renormalization. Analogous to the renormalizations of field theories, these finite renormalizations deal with effective infinities instead of infinite infinities.