eGPUs are massive, and not portable at all. Some people have to bring their laptops other places besides their desk.
Well it's certainly a question of what you think is massive, but to my notion the eGPU solution for the Razer is not something I consider "massive":

It might not be for everyone, but for on the road I'd say that you'd manage with the 580. Of course, if you're a video professional you'd need to bring the eGPU with you, but getting a bag to carry that together with the laptop would not be a big deal, and probably nothing that would happen very often. If you're a regular traveling video professional, I think you have a lot of other heavy duty equipment that is more of a burden.
Can't really think of a situation where the loss of the dGPU would be a constraint. Working from a café I don't think you'd do very much (professional) video work. At home or at the office an eGPU would be better and with tenfold performance compared to the dGPU.