It's... pretty dumb to discuss if aim or accuracy is more "important" or more of a "core" of the gameplay...
The amount of skill required for either one is completely different by each map.
I do believe combo multiplier is pretty broken at its current state. Like it was mentioned earlier, a run with ONE miss, can have completely different scores depending on which point of the song the combo was broken. If it was the first note or the last note, it would be the equivalent of getting a score with one less note. However, if you miss in the middle of the song, your score suffers a lot. Accuracy also starts to matter a lot more later in the song, because a 100 done in the beginning of the song with a small combo count has a completely different score worth than a 100 done near the end of the song, when the combo is a lot higher.
You really can't defend this flaw.
Thankfully, ppv2 doesn't take score or rank into count at all anymore. A tiny combo break is nearly un-punishable.