I agree the monochrome icons have significant disadvantages. Visual Studio a few years ago made the same attempt at having monochrome icons and there was such pushback that they eventually moved to the current scheme of "monochrome with a splash of colour", which I think is way better.

That said, Photoshop also uses monochrome icons and it can help in some ways to avoid distracting from the image which you are working on. I am not sure what the best compromise would be.