It's unfortunately pretty sensitive to that. Dropping chest value to 0 gives a max ROI of 11%. That said, other than soulbound cards, everything in the chest has a pretty well-defined value (SPS has a market, potions can be directly bought, even merits can be minimally exchanged for DEC if you burn the cards), but the soulbound cards don't really have this.

If I just drop the soulbound cards' value to 0, I get a max ROI of 100%. So fortunately it's not super sensitive to the value of the soulbound cards themselves, which were the most unknown part.