Backstab was changed to sneak attack in 3.0. Rogues are still the only class with sneak attack in BG3. Backstab in BG3 has nothing to do with 2nd ed backstabbing. It's not an equivalent kind of ability. There's no reason to say no class but rogues should get Backstab advantage just because Thieves had a completely different ability I 2nd ed that was called backstab. That's just... it doesn't even enter into the computation. It's irrelevant.
The thing is there's nothing special about a rogue in this game because of how busted flanking is atm where everyone just bunny hops to each other back's like froggers. Which is why melee feels also stupid. Stuff like that is what is trivializing classes in general. Just having a reskinned and slightly different version of the same class and calling it other class doesn't cut it up for me.
Rogues have sneak attack. Nobody else has sneak attack.
And like the other martial classes, flame dip, oil of sharpness, wyvern's potion to add another ~15-21 damage to your attacks, and dual wielding classes attack twice to boot to trigger the effects of burn dipping and poison coating. Plus surprise attacks from stealth provide a guaranteed crit.
The problem with casters is their hit rates on their spells are worse no matter what, and most importantly the consumables and weapon coating effects that break melee don't affect caster spells at all.
In fact, I'd say what really drives this huge gap is consumables.
In every solo cheese video you've seen, fire dipping, poison coating, invis pots, oil of sharpness, potion of speed, and wyvern or basic potion are used to completely trivialize encounters just as much as stealth cheese and pushing creatures off walls.
