many marketplaces uses the attributes from the main level, for example, OpenSea, but lately, also Elrond added an example in the docs with attributes in the root level
ERC-1155 has the properties field: https://eips.ethereum.org/EIPS/eip-1155#metadata I like this idea, and IMO the attributes should also land there as it is now, but the tool should generate the output which will suit best for marketplaces
Reasoning: