the base could be a trained component like muscle strength

If it worked like that, there’s still the question of “what component?” Muscles becoming stronger as a result of exercising them is a complex behavior, governed by many genes. Harry’s reasoning towards one “magic marker gene” suggests that is not the case.

I can think of all sorts of possible explanations, I just can’t see one that looks really reasonable; since we have no actual explanation about how stuff works, you need a lot of assumptions for anything and stuff tends to be arbitrary. If you think about it, all substances being combinations of four elements, or Lamarckian inheritance, are plausible explanations if your only observations are on the level of “some stuff burns” and “water quenches fire” or “children kinda look like parents”.

(“Inventing” new charms is mentioned several times, but there are basically no details about how that works. Harry just changes how to apply a couple of existing charms, and he seems to have figured out how he might pick ingredients for potions, but even there he’s not told where the gestures and ritual come from.)