Mobile GPUs are vastly underrated compared to their desktop counterparts. The reason is they have somewhat lower performance than the equivalent desktop one (since they have to work on a tighter power and thermal budget) and a laptop will always cost much more for the performance they provide than the desktop equivalent. However, if you forget about the price difference and see only on the efficiency front, you will see the laptop GPUs often outperform the desktop equivalent.
Inversely however, price is a big factor for most and if you can sacrifice the mobility, there's no denying, the desktop is superior.
Here's a comparison between the GTX 965m with the GTX 960.
http/www.tomshardware.com/reviews/nvidia-geforce-gtx-960,4038-4.html
http
/www.notebookcheck.net/NVIDIA-GeForce-GTX-965M.134120.0.html
You can see though the 960 is logically inferior than the 965m, its performance is much superior, not to mention the system with the 960 will be vastly cheaper than a laptop with the 965m.
So yes, mobile GPUs are very capable, but at the same time very expensive.
Anandtech came up with a good article regarding this. Read it
http/www.anandtech.com/show/7287/analyzing-the-price-of-mobility-desktops-vs-laptops