Yes. I agree. A real 2d painting program still provides some more features, all these filters, tools for off-setting, scaling, copying, whatever.
I will not replace GIMP. But a 3d painting tool has a lot of advantages as well: you can paint over uv-seams/borders. You have real-time feedback and you can apply textures very accurate while some distortion could happen if you use a 2d picture and a slightly distorted uv-map.

So a combination of both is just perfect. In the past I painted most parts of textures in GIMP and I used Bodypaint 3d only for minor tasks like repairing the uv-borders. But I am sure I will paint more in Modo because it is so easy there.
The same counts for sculpting. I do not like the ZBrush interface but I can arrange with it. But sculpting in Modo is more easy, more intuitive. ZBrush always appeared a bit like magic to me, like a black box. I understand how to handle but don't know how it works. In Modo it is fairly simple. I have the impression to understand it all.
But I am not afraid to use ZBrush as well if I need even more details.

But that is only me. Maybe some other people see it the other way around.