You can make the same argument about Minecraft since servers download you texture packs, data packs or skins. I don't think that Apple should stop these apps, that's their game model.
They are called "Behavior Packs": https://learn.microsoft.com/en-us/minecraft/creator/document...
You can purchase content that runs behavior packs from the store, but it's all through soft currency purchased with per-platform stores.
Link to some of the content: https://www.minecraft.net/en-us/catalog
As for the "not as powerful as Roblox", we're working on it :)