It's my understanding that the browsers use a translation layer (such as ANGLE) between both WebGL and WebGPU and a preferred lower level native API (Vulkan or Metal). In this regard I don't believe WebGL has any more or less protection than WebGPU. It's not right to confuse abstraction with a layer of security.
My analogy was bad and I'd probably be wrong as you (and your sibling post) say to expect WebGPU to have any lurking dangers as compared to WebGL. I was mainly trying to express concern with new APIs and capabilities being regularly added, and the danger inherent in growing these surfaces.
