Morphological Gradient Versus Linear Gradient in Image Processing
I've spent few years working with specialists on mathematical morphology, and I didn't get a mathematical answer why morphological gradient was better than a classical convolution. It was more a choice of ideology.

However, the results are a little bit different and according to the problem, you can choose one over the other.

But morphological gradient is super fast, because it is usually performed with a small structuring element (radius 1 or 2) of type square or hexagon, so you can use SIMD/SSE optimization.