> a few € for a transaction of ... a few € for a cheap indie game
that's misinformation. A lot of mainstream cryptos are incredibly cheap to use, compared to credit card. I mean, credit card has basically a guaranteed 0.35€ fee on every purchase which is just insane for small games.
Examples like LTC, BCH, XMR... have really low fees. ETH is also now on Proof of Stake so it pretty much uses no power.