I think multi-currency systems can be used to juice microtransactions pretty hard still. For example League of
Legends gives players free "chests" and free "keys" as a slow-drip, and you can open any chest with a key to get some random loot. If your chest count doesn't match your keys you can buy more of either using real cash. So basically multi currency systems can be used to keep players intentionally in a state of imbalance. It also makes it so their money doesn't go as far in the game if you have to buy separate blue yellow and red coins instead of just yellow coins like it sounds like in your Hades example (just having 9).
Sure, but multi-currency systems juice anything. Control, for example, has tons of different materials used for upgrades and crafting. In order to get the right mix of upgrades, you have to travel to all different parts of the game world. Nier has something similar.
By comparison, there are plenty of games (especially older ones) with only one or two currencies. Maybe you just find the one place in the game world that lets you grind out those currencies the fastest, and you do that over and over until you’re sick of it.
