I think the EmuDeck compressor is for compressing to emulator supported formats, like the RVZ format used in Dolphin for example. I'm not sure how it compares to btrfs, but RVZ is supposed to keep good performance while compressing garbage data in a way that maintains compatibility.

EmuDeck compressor is not simply compressing games, it is converting them to more efficient formats (i.e. instead of a raw disk image, it removes the sectors of the images that are effectively unused)