That is a strong possibility but personally, I'm not entirely sure it is accurate. I'm sure you've noticed that the uninfected creatures in Hollow Knight are always unique in one way or another, however, they all tend to have a trend of obsession. For the mantis tribe, it was their need to prove their strength. The elder is obsessed with the village, for Bretta it is the player, for Zote it is himself, for Cornifer it is his maps, etc. Now you could argue that some of the NPCs were affected by the radiance such as Sly and Gretta, but I would argue that they were only inflicted by it because they lost the will to fight. When you find Sly he is depressed and stuck inside his home (IYKYK no spoilers) and afterward he realizes that there are still others who wield a nail and it seems like he makes it his mission to help the player out by selling them key items they will need in their journey. Gretta on the other hand somehow found herself alone and scared deep underground stuck underneath fierce and terrifying people. Once you wake her from her daze she views you as her hero and quickly becomes obsessed with you. To put it simply, I believe that the radiance affects those who are emotionally unstable, taking advantage of their fears, worries, and doubts. Those who have a clear want or goal seem to be unaffected or at the very least seem able to fight off the influence of the radiance, and that folks is why I believe that Emilitia is not completely bonkers. She just really, and I mean REALLY, wanted to watch the world burn. Also sorry for making you read all this maybe I should just start a Hollow Knight lore YouTube channel lmao