Lighter foils/decks make tricks with the foils easier. Not speaking of carrying them
I believe aluminum mast/fuselage could be as efficient and smooth as carbon and many people macgyver pretty wings/fuselage to aluminum mast and save themselves $500-$800 easily.
Some people argue that inertia of heavy setup is good for riding, which some can also speculate about heavy twintips, heavy kites, heavy pickup trucks or heavy spouses. I'm skeptic about each of these. I love carbon and I love flying the foil.
Just came back from 2 weeks in La Ventana where one of the guys on our crew, who has been riding H5 hoverglide setup for a year ad a half, put his feet on 633 and we couldn't pull him off that board, and we just sat and smiled telling him that there's a reason to ride carbon - the material is just expensive enough to justify manufacturing better foil out of it.
I think Axis makes pretty aluminum foils, but they're not cheap, making no reason to not buy carbon.
You can get a brand new Moses 548 setup with 71cm mast for about $1100, why bother with aluminum set for $900