Advantage isn't given often enough in core 5E. I'm a fan of how available it is in this one. It feels like something you can actually get if you just use your surrounding and circumstances, as opposed to something you can only get when you bribe the DM.
It is because the core 5e follows restrictly the design of bounded accuracy, and adding more tactical aspect to combat. You need to shove someone prone, or use spells like Faerie Fire to get advantage, not brainlessly walk to someone's back since advantage is very very strong. While here it's just free for melee attackers. What you said about using surrounding and circumstances is valid for high ground, but not for backstabbing. You DONT need surrounding or circumstiance to get backstab, you JUST walk behind a dude and attack him, no AoO, no resource, just free.
