with regards to the differing hitboxes and falling speeds ... only a portion of the cast heavily relies on character specific combos; there are characters that can get by with universal combos (ahem, potemkin). aside from that, adjusting to hitboxes and weights just comes with experience. eventually you get a feel for the spacing and if you're in control of your character, you can sort of make combos on the fly.
but yes, "experience" is what it comes down to, cause one of the hardest thing about accent core has always been match-up experience.
and honestly, execution wise, accent core really isn't hard aside from a few characters (e.g. i-no). there are other fighting games that are more execution intensive than accent core. at most it requires a small amount of time in training mode as your initial investment. every character does have "hard" combos (even potemkin), but they're generally not necessary to win.