well my previous test the files are 2.4GB a game folder textures only. I see your speed/compression (very nice) and your test files are 120MB and looks like the files can´t be compressed more than a half. dead island its a good game to test compression also GRID too, because the textures files are very kind to be compressed.
i forgot to add exe and delta algos to zstd test
because fb -m4 use those algos.
Pd: you have right felice level 6 its the correct level to compare instead level 21.
PD2:
Here the others tools for test.