I don't believe the blessing of light is actually gone.

My understanding is that the chosen warrior of light is being tested by Midgardsormr.

Reason I say this is because Midgardsormr tells us we are not gifted, we are chosen. After he "seals" the blessing he says he will watch what we do.

Furthermore the blessing of light is what allows us to fight the primals.

Lastly it may as well be that Midgardsormr is actually protecting Hydelyn. The Ascian did mention she is getting weaker.