This was a really great writeup and an amazing way to present it.
My hunch is, there is another dark pattern hidden which he didn't discuss yet: the quantities in which you buy gems. You'll often land just one or two gems short of the number you actually needed. Then you can either buy the 3 gem pack for the worst relative price or buy another larger pack, encouraging you to come back later.
It seems hard to really spend all your gems and come out at zero. Usually there is a small amount left that on its own is useless but lures you into buying more.
This is a fairly common tactic when you have intermediate in-game currencies that you actually use to buy stuff in the game. For example, you can only use gems to buy stuff in-game, and most items in-game are worth a multiple of 200 gems. But when you buy the gems with cash, they're somehow only offered in multiples of 500 that are also not multiples of 200. You end up buying a few extra that maybe you didn't want, and they can later hook you in with the 'well, you already have some in your wallet' approach.
My hunch is, there is another dark pattern hidden which he didn't discuss yet: the quantities in which you buy gems. You'll often land just one or two gems short of the number you actually needed. Then you can either buy the 3 gem pack for the worst relative price or buy another larger pack, encouraging you to come back later.
It seems hard to really spend all your gems and come out at zero. Usually there is a small amount left that on its own is useless but lures you into buying more.