Sight cones are not supported by D&D 5e, thus the whole perception and stealth system got broken by their introduction and made worse by having sneaking characters not being locked in turnbase and on top of that the whole shift in game balance by turning jump/shove/hide into bonus actions for every class.
Implementing the actual rules from D&D 5e would 'surprisingly' solve the problem. You can hide in combat, but not in plain sight. Perception is 360 and you actually roll for stealth not trusting on you noisy heavy armour to sneak up on someone who is just looking the other way.
I confess I don’t know the detail of how 5e handles stealth, but in general I’m in favour of BG3 implementing 5e rules as written unless there’s a compelling reason why not. So from that perspective I have no argument with what you say.
Speaking purely from the perspective of playing BG3, though, I do think the sight cones can be a useful representation of what is in plain sight and it makes sense that hiding there is harder (and might even be impossible in certain situations). But it doesn’t make sense that it’s only in their sight cones that NPCs can detect us, so I do hope that Larian will also introduce a 360 degree perception check that’s influenced by things like whether the sneaker is wearing heavier armour, that would bring the mechanic closer to 5e.
