Larian reversing their backstab/flanking advantage homebrew could be indicative of them working on the Barbarian and arriving at a very late epiphany that they were screwing Barbarians and their Reckless Attack over with it. On the other hand, it could also be that Larian simply realized their homebrew promoted shitty gameplay, but given their fondness for adding way too many highly questionable homebrew additions - the former is more likely.
It wasent homebrew. It was a literal interpretation of the rules. If you attack someone who cant see you (for example if you are behind them) you have advantage.
Standing behind someone doesn't mean they can't see you. PHB pg 177: "In combat, most creatures stay alert for signs of danger all around, so if you come out of hiding and approach a creature, it usually sees you" and "you can't hide from a creature that can see you."
The DMG has
optional rules for Facing, further clarifying that according to base rules a creature is assumed to be constantly looking in every direction. And Larian's implementation didn't include all of the other components of this optional rule, such as using a reaction to change the direction you're facing.
RAW, even standing behind total cover doesn't grant you advantage on your next attack. You have to specifically take the Hide action in order to be hidden, and only a successful Stealth check against the enemy's passive perception will you get advantage on your attack.
These are seperate things. Beeing aware of someone and SEEING them are not the same thing. If im in the aisle at my local super market and I can hear someone behind me in the que, I know the person is there. I cant see them though because I dont have eyes in the back of my head.
Generally speaking at tables DM's will rule that unless you were hidden when combat started they will be aware of you. But RAW nothing in the rules prevent the whole 'stand behind a person and they cant see you' bit. The optional rules for facing are just that. Optional. Without them there is no such thing as facing or outflanking. Rogues dont need to outflank or be behind a character to do suprise attacks either. Another target hostile to their target within 5 feet is enough in 5th ed.
Page 177 refers to beeing hidden and covers ambushes more then anything else. Its rules for use of stealth. How to stay hidden and how you can lose it. Attack someone from hiding and you got a turn of suprise combat, which is devastating I might add; which is the main reason why players might want to do it.
Page 195 top left (part of the 'unseen attackers and targets' section handles attacking someone who cant see you: "When a creature can't see you, you have advantage on the attack."
When you attack someone while invisible for example you still have advantage. Because they cant see you. If you lose invisibility after the attack you dont keep the benefit, but thats besides the point. People can be aware of your presence and still get hit by advantage because they cant see you. Likewise, people can be aware of you but be blinded. Same thing, they might hear you or heck even smell you. But they cant SEE you. Advantage on the attack.
So uhm. No. Larian had it right and every group that says that people attacking others from the rear dont get disadvantage are actually house ruling it. If you go strictly by whats written. But every DM is free to play it as they feel fit. Just moving behind a person and getting free advantage is way to powerfull id say so I agree with them toning it down. But RAW. They had it right.
