POW has a fair chunk of pushback - however it does offer unique properties. The general preferred approach is pay-to-relay.
It’s a good point that perhaps generic messages shouldn’t be posted to dedicated public human consumption relays to begin with - but again, you can’t really control this. However, pay-to-relay could assist - but people will just pay for their bot pubkeys to relay, as it’s cheap per event in general.
A counter point is, just like advertising and tagging, as soon as it’s used for discovery, people will do whatever they get to boost/maximise their discovery for the lowest cost. Bot dedicated relays for example likely wouldn’t get as much attention or engagement.
I see kind 1 as a forever dumping ground of random events, as it will be the most supported kind by apps and get the most eyes. Our engineering challenge is to best manage that.