TL;DR I think RAW 5e stealth would work fine with little playtesting needed and leave Stealth and ambushes as a rewarding option for characters who choose to specialize in it.
I have no objection to the rules you put forth, or 5e raw rules. Still, I think any stealth ruleset would require a non trivial amount of design work.
Consider the fact that Bg3 doesn’t do group stealth checks. If the party tries to sneak around some guards, because sneaking outside cone of vision isn’t an auto success, every one rolls for stealth individually. That includes the plate-wearing, disadvantage-rolling paladin. The party’s stealth effectively becomes the stealth of the least dextrous, which doesn’t feel great.
So then maybe Larian adds group stealth checks? But how does the game know what a group is? Do we have to fiddle with the portraits? In any case, these questions and more would need answering.
