This is a crazy problem of cat and mouse. I decided to keep 2 complete RF sets of these cards and was burning all my extra singles. Now I'm not even sure if I will ever unlock these cards because the buyers may not exist and few people will want these cards when they rotate to Wild in less than a year.
I didn't buy anything off the market either. I made a few p2p deals to buy the few GFL cards I was missing like BCX of Skok, Iziar, and Hulk. Mostly I just swapped with other people cards of equal rarity, so we were just paying the same fee to unlock GF cards and swap them. I even sold a few cards to buddies for credits since they didn't want to bother with buying the DEC themselves.
Splinterlands perhaps has this flaw of handing out too many rewards in the form of cards, and then trying to repent by creating other things. There are still two active collections to be sold Chaos Legion and Riftwatchers and they still tend to try to create more things for Rebellion. A real flood.