60 second explanation of the three APIs:
WebGL 1: vertices and triangles are stored on the global GL context object and need to be rebuilt every frame. Shader language is a very goofy, somewhat obnoxious GLSL lookalike. You can write vertex and fragment shaders, which are the necessary ones to render, but also the least interesting. Post-processing is a serious pain. FPS is limited by bandwidth to submit to the GPU and CPU usage can be stupid high.
WebGL 2: improved shader language (much more similar to GLSL, better compilation, better branching), still only two pipeline stages. Render buffers, depth buffers, multidraw, allowing for modern techniques like deferred rendering and efficient shadowmaps. Vertex attribute buffers are their own thing amd dont have to be freshened for every draw call. At this point webGL is similar-ish to native opengl with a bunch of missing features. In webGL 1 you had to do things very differently from a native api, which was very slow, messy, and annoying.
WebGPU:Vulkan came out! And everyone learned that oh, actually having everything on a single thread really sucks, huh. OpenGL has a global context that prevents great threading- have to make draws from a single thread, even if you can construct buffers etc in job threads (minor improvement) you have to sync back. Vulkan and webGPU let you submit to command buffers with their own contexts. In WebGL 1 you had to rebuild and rebind all of an object's vertices every time it had a drawcall. In WebGL 2 you built them once and just have to rebind each one in series for every frame. In WebGPU, you can bind in parallel from webworkers. Not ideal parallelism, but shockingly good for javascript. For some things like shaders, you don't even need to recompile, which is a hard-to-avoid main thread blocker in WebGL 1/2.
WebGPU can also do compute, which rules- many complex AAA techniques really require this and don't work on WebGL because it wants to send all its render buffers back to the CPU.
