This is probably an unpopular opinion, but I actually don't think the referral/ad model is that bad of a revenue model for products like a social network, HOWEVER, that's only if the ads don't involve:

1. Data collection on the user in order to target the ads

2. Excessive frequency of ads

3. Disruptive placement of ads in the interface that get in the way

I think at their best, ads that are done correctly and don't do those 3 things are essentially a product discovery/recommendation tool for users that also allow their nostr client to remain free.