Larian needed to have their own vision cone mechanic instead of D&D stealth.
I feel Larian likes to bite more then they can chew.
This is a cool addition - a detailed mechanic like that is more interesting to interact with then just abstract “roll to stay hidden”. Add to that Thief-like environment interactions (dousing light sources) and we have a promise of genuine stealth experience. Except it’s all broken and doesn’t work, as stealth games don’t design themselves. It’s not a functional stealth-system in itself, and it creates issues with already existing, complete systems like combat.