To be fair when it comes to creating 2d textures photoshop is way ahead of blender, so is gimp for that matter. Brushes, layers, filters etc. It is not just photo editing it is also about creating 2d art.
Hopefully one day Blender will incorporate these things in texture paint and there will be no need to swap around software. I am sure it will – one day! There is a thread here on Blender Artists discussing exactly that, and taking it further with nodes and modifiers.
What is true is that 2d art programs have not progressed in the way Blender does. They still do basically what they did 15 years ago. 15 years of blender development has had huge changes.