Well, the Walker as a dedicated skill is indeed one of the most powerful ones in Lemmings (especially the fan remake “NeoLemmix”), in particular for cancelling other skills and turning lemmings around.
Applied to BG3, this skill-cancelling would include things like kidnapping characters by picking them up and cancelling the throw / improvised melee attack action — and we all know how broken that gets.

The main thing that would make a Lemming playthrough of
BG3 even possible is the game Lemmings 2: The Tribes, which added a bunch of new (and oftentimes redundant) skills, including the Fencer, which would allow a lemming in BG3 to use swords and rapiers.
In vanilla Lemmings, the most powerful skill is the Builder, which creates a staircase — or, in BG3, a box tower.
