It is difficult to compare. I know of at least 1 OpenGL ES 2.0 implementation where “compilation” consists of making a copy of the shader source. Everything else is done at link time. I have no idea if the same is true of the vendor’s OpenGL ES 3 implementation. (The vendor is not one of the ones you tested.) I think the only way to make a valid comparison between implementations is to compare the sum of compile and link times.
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