[Kyrottimus]

A Devastated realm's players, using the words posted in the OP, seems that

"...will not provide..." i.e. "give out" RPs and Warmaster quest credit.

This means those players of the Devastated realm are not worth any RP's or Warmaster Quest points to either of the other two realms.

Example:

Alsius night crew is getting invaded by ignis, and loses its gems. After the invasion, Alsius is "Devastated" and Syrtis captures Imperia. However, Syrtis players will not get any RP's or credit towards warmaster quests from killing Alsius players while Alsius is Devastated.

Just using the existing language here in the original post, I have no insights to this new feature, am just interpreting the literal context of the used English.

-Kyro