Much more decentralized. And for some cases, you can’t always use the trusted peers approach. For example, say you want to do this for BitTorrent as well: map info_hash:start_offset:end_offset to IPFS CID. Where’s your trusted peer now?
Storing each mapping along with a bunch of signatures could get very expensive.
How do you mean? A signature is 256 bytes large for a 2048 bit key. You just need 1 signature for each node, each node could sign a merkle root of all their asserted mappings. This is no huge amount of metadata in any case, even if they sign each mapping individually.