Cores make great sense where they add to the
boat and a horror where misused by the
builder, or when mistreated by ex-owners.
I have seen some designers and builders move away from hulls cored below waterline. They still seem very happy with topsides and decks.
Personally, I do not like cored decks as ex owners tend to drill holes everywhere and that's how your nightmare starts. We have one.
b.