One way to look at it is WebGL is OpenGL ES 2.0 and OpenGL ES 2.0 is OpenGL with all the legacy cruft removed.
Since shaders were added all the legacy fixed function pipeline
glVertex etc all made no sense to keep around.
So are those "missing" features or correctly and properly "deprecated" features?
What specific features are you looking for?
WebGL/OpenGL ES 2.0 is basic vertex and fragment shaders. There's limited support for non-power-of-2 textures and only a few texture formats (not really much of a limit is 99% of all textures are RGB8 or RGBA8). Support for floating point textures is optional but the majority of devices support them. Support for rendering to floating point textures is rarer though. Few if any mobile devices support rendering to a floating point texture.
WebGL2 (just shipped) and OpenGL ES 3.0 added a ton of new texture formats including integer based texture and 3D textures. It removed the non-power-of-2 texture limits. It added transform feedback (the ability for a vertex shader to write to a buffer). It also added occlusion queries. Vertex Array Objects are standard (they were optional in WebGL/ES 3.0). There's a bunch of other more minor features.
ES 3.1 (and probably the next version of WebGL) adds compute shaders (the ability for a fragment shader to do random access writes). Fragment shaders could only write to the fragment/pixel being requested of them at the moment whereas compute shaders and write anywhere they want.
What other features did you want to use?