Like everything in the universe, there are no solutions, only trade offs.

WoT relays are not a magic bullet, there are one way to fight spam that come with trade offs. 

Some relays will fight spam with WoT, with NIP05, with PoW, with a paywall, with pattern matching, with AI etc...

Decentralization is messy and we will likely net out with some mosaic of relays that all use different techniques.

But one thing is for damned sure: relays must fight spam otherwise their hard drives will eventually explode. The idea that relays should just store and distribute every single note and let the client decide how to filter all spam has to be one of the dumbest ideas I've heard from people on nostr so far. Maybe this seems feasible since we only have a few attackers right now, but eventually we will have hundreds.

If you really believe this, I invite you to run a completely open relay and see how well it goes for you.