Every power build gets 3 levels in rogue for its subclass features and then ignores the class because sneak attacks do not scale.
They do scale. Their damage die increases with every other Rogue level (I.e. Levels 1, 3, 5, 7, 9 and 11). Meaning they go from 1d6 at level 1 to 6d6 at level 11.
The only major drawback to Rogue is in regards to Haste, where Larian's homebrew on non-Honour Mode difficulties makes other classes exceedingly broken. I.e. Instead of the actual 5e Haste that grants one additional weapon attack. Larian's Haste gives one additional Standard Action - Meaning that Extra Attack martials gets 2-3 extra attacks and Casters get an extra spell cast. This is compounded upon by the ever prevalent Elixirs of Strength, so each of these extra attacks are getting massive Str modifier bonuses (While Sneak Attacks don't have any stat modifiers included). Honour Mode helps bring this back in line by only providing Martials with one extra attack (Though Casters still get their bonus spell cast unlike true 5e Haste)
Ironically, even the reason why everyone multiclasses Thief is due to Larian's homebrew too. Where Fast Hands is granting straight up extra Bonus Action compared to 5e's actual rules that simply lets a Thief use certain items with a Bonus Action (Which would still be pretty strong in BG3 given the abundance of Smokepowder Bombs/Satchels they'd be able to throw with a Bonus Action. Where normal campaigns don't have such available items and would instead rely on things like Alchemist's Fire, Acid Vials and Caltrops)
While the reason why leveling Thief beyond 3 is not done being because everyone is going Str builds because of Elixirs, so Sneak Attacks don't even function because they require Finesse weapons (As there's no Thug subclass in PHB that provides Sneak Attack functionality for non-Finesse weapons)
Essentially, Sneak Attacks and as a consequence, Pure Rogue, only feels weak due to Larian's homebrew massively powering up other builds. They could add more homebrew to boost Rogues, though this could result in having Rogues feel broken compared to non-busted builds (Not everyone powergames with Hasted Fighters/Monks with perma-Cloud Giant Elixirs or Bards tossing out Arrows of Many Targets Flourishes or whatever other min/maxed builds you can think of. Within the context of "Normal" builds, Rogue is fine comparatively)