Some people think they can use NIP-32 labels "L" and "l" as key-value pairs to be queried on relays as if they were MongoDB instances.

That was never the purpose of NIP-32 and doing this is not going to work in the long term and will only lead to centralization and proprietary protocols, not standards, built on top of Nostr.

Specific, hardcoded kinds and tags, is infinitely better.