This feels like a strange collaboration. In my view, GOG is all about owning the things you purchase. Amazon on the other hand, has a reputation of randomly banning people when you trigger any of their algorithms (such as the shipping company losing your package at their terminal). You lose all your purchased digital content as well as any existing balance.
I get that in this case you'll still have your GOG content at GOG (hopefully) but Luna still seems to require an Amazon account. I would go out of my way to avoid having any dependency on Amazon.
This is exactly why this collaboration is good. You don't buy anything permanent from the unreliable monopolists like Amazon or Google with zero customer support, you just pay them for service as long as it is needed and get to keep all your purchases at a more reliable corpo.
Yeah, it seems really weird to me as well. But as long as this is a side effort and doesn't affect GOG's existing model, I don't care because I can completely ignore that the cloud gaming aspect exists.
I get that in this case you'll still have your GOG content at GOG (hopefully) but Luna still seems to require an Amazon account. I would go out of my way to avoid having any dependency on Amazon.
I guess it's neat until it isn't though.