There's theory and there's practicallity.
Theoretically Libre relay makes the filter useless.
Practically, this is either not fully known or understood by everyone... and this is why they are using out of band methods which hurts decentralization.
And by hurting decentralization, I mean only allowing well known miners and pools to capitalize on high fee paying non standard transactions, giving those miners an economic advantage... Theoretically.
The amount of extra money spam miners get is very small relative to their total profit. But the effect on spammers is massive in proportion to their total expenses, because fees are nearly their "only" expense. By doubling or tripling the effective costs of producing spam, there is an asymmetric positive effect: the spammers get relatively poorer much faster than the spam miners get relatively richer. This asymmetry makes the filters worth it imo.
