Uh, that would be deceiving marketing, a 1kg spool should contain 1kg of filament…
But hey, maybe my view on this is a bit warped because I only buy filament from reputable brands (and usually from their own store) and not from marketplaces like “big A” where hundreds of sellers battle to be the cheapest.
If companies that still used plastic spools are starting to switch to cardboard, I think that’s a good thing. Not only is it easier to recycle, but probably also lighter (your typical 1kg filament spool weighs around 200-300g), so the bulk should save some fuel for transportation.
Though I personally prefer using no spool at all (during shipping) 😉 Wherever possible I buy Masterspool refills.
Definitely better than the usual full plastic spool, but IMHO a step back from “true” masterspool refills. I’ve already printed my MS spools, switching in a new refill is easy enough, and I never bother to store an already opened refill without a spool since I store all of my filament in a drybox anyway.