No, we don't need a relay for every thing (and every combination of two or more things), just like we don't have a website today with a community for every thing, but we have some because someone did them and they succeeded, while others were never tried and others failed, and we're still ok.

I think having Nostr and the universal relay as a standard makes it much easier for more of these niche relays to exist, so we'll end up with a lot more stuff.

Again, I'm not saying the WoT approach shouldn't exist, it definitely should, and both approaches can be combined. I'm just saying we shouldn't decide on that being the only solution, because it's quite complicated and we can't be sure it will scale across the vast spaces of humanity and relationships (and computer resources for downloading and processing all the data).