Aluminium core in jump ski's (water)has worked great for 30 years.
Aircraft/F1/18foot skiffs( when in their expensive mode)/water skis,thats the order for common usage of new composites as far as I can tell.
As for cheap composites that would be production recreational boat building where anyone can do anything they like.
( like use balsa with polyester non bagged layup)
Boat builders are not necessarily Boat designers who are not necessarily Engineers who are not builders who are not designers.....