Some NFTs hold value but to say just because something is an NFT means its value will hold is simply not true. Splinterlands cards all have a use case. At the very least, each NFT card can be used to play the game.
Also I'd like to point out that your experience with SPL cards specifically is what you would classify as anecdotal evidence.
Well of course there is a lot of garbage NFTs as well. However there are a lot of legitimate cases. This goes the same for any type of asset including artwork would be the best example of this. Some artwork is priced at stupid high speculation prices while others are low all because of the name and history of it all. Goes for card collecting as well many cases so it's really no different than any of those assets.