All classes aren't supposed to be able to backstab, that's another big issue that trivializes the whole Class System which is almost as fake as the one they have in DOS2. You even have backstabbing bears here.
What? Backstab is just Larians take on the flanking rules.
By the rules, [i]no[/] class is supposed to be able to backstab. Backstabbing is something Larian has added, not something they've moved from one class to all.
I actually think it's Larian's implementation on the combat facing rules (from chapter 8 of the Dungeon Master's Guide). Basically, shield bonus only applies to attacks from the front or the same side of the shield, and attacks from behind have advantage.
It's an obscure variant rule that few tables actually use, but it's technically a legit D&D 5e mechanic.
