(noob speaking)
Challenge get's you used to input. Yes, it's impractical but many of the combos you see are derived, I feel, from Challenge mode. You also get inspiration from them anyway. In terms of getting away from button mashing, I think this is the cure.
However, timing wise, I really think fighting against Lv 100 comp is the best way... I mean, fighting against people is not the same as Computer, but you still get the general idea to what to look out for, your timing of moves, what moves are actually vulnerable, and blocking strings (basic). I mean sure, I practiced at times with Arakune, having full curse meter, and having it NEVER run out (yea, that's not fun). It's DEFINITELY impractical, but I do get the hint of how the pro Arakune does their scary scary combo -and how to run away, slip through (not really, but I have beaten the comp 2 out of 10 times).