I think the Azem crystal summoning thing can technically "run out" so the WoL tries not using it too much?
However:
In Stormblood, before the Susano fight (i think?), Alisae jokes about the WoL just summoning random friends they have around somewhere.
There are other parts in the game where its implied that the WoL just stomped the current local god by themselves.
Both solutions worked equally well I find. A healthy mix of every explanation we have would be nice.