PoW doesn't stop event aggregation. Event aggregation of valid events with PoW, can become a denial-of-service attack. Most relays don't want to host every event from everywhere, but clients want them to so that they only need to connect to that one relay.

Charging LN is also going to need to be done in a way that doesn't just look at the pubkey of the author, but uses protocol messaging to ensure that the author is the one trying to host the event, and not someone else replicating it.