Even simplest (in terms of graphics) 2D games like Balatro have custom shaders today. It's an extremely valuable, and commonly applied skill set among game devs.

> game engines... all the possible style choices

Nah. Nope. Never happens.

Game engines might have node-based shader editors, but they're roughly as low-level as GLSL.

Honestly I don't even know whether I'd call GLSL shaders "low-level." When I hear of low-level graphic code I'd imaging one's talking about managing pipeline state objects manually or something.