The first thing the quote evoked for me was this other quote from the Diagram
"You must be king. Of Everything"
T. is unifying the world "He had taken the first major step toward unifying the world"
The KR will somehow hindered him in his plan, his only option will be to get rid of them, He asked for the capacity to save the world, he is convinced that he is the only one that will prevent the Desolation, whether he is right or not..
"If he was going to trust one thing to believe in, it would be himself and the raw genius of a human mind unfettered"
it doesn't mean there are no one that could also have that capacity, like the KR,
I don't think the Radiants are causing the Desolations, it's said somewhere that the spren bonded with humans after the exemple of the Heralds, the first Desolation could not have Radiants,so it can't have a link.
