[DAV Spoilers] Question About the Old Gods

This is something I'm hung up on...

We're told or led to believe the Evanuris were whispering to the Magisters Sidereal through the Old Gods, but we're also told or led to believe the Evanuris were in uthenera after Solas locked them away.

If we assume the Evanuris were conscious enough of events beyond the Veil to begin whispering through the Old Gods, then once the first Blight ended in failure--which coincided with Dirthamen's death or his becoming incapacitated--why would the other Evanuris launch Blight after Blight only to see it end in failure?

I thought maybe it could be that Elgar'nan was doing all the whispering himself on behalf of the other Evanuris after figuring out their life forces were powering the Veil. Though he seems to show genuine care for Ghilan'nain, I tend to believe Elgar'nan would sacrifice anything or anyone for his own personal freedom. But we know it couldn't have been Elgar'nan pulling the strings because it's stated plainly that both he and Ghilan'nain were in uthenera during imprisonment.

It just doesn't make sense to me that the Evanuris would knowingly risk death after two or three failures (they had to have known after the Third Blight that it wasn't a viable strategy).

So the only conclusion I can reach is that it wasn't the Evanuris whispering through the Old Gods; it was the Executors. But maybe I missed something. Was this ever resolved in Veilguard?

EDIT: It might not be clear from my wording, but I'm aware that the Magisters Sidereal and the Blights are separate events. The question I have is about the relationship between the Evanuris and the Old Gods, and ultimately why they would risk the Blights since the Old Gods, as archdemons, literally contained their immortality.