I'd be incredibly surprised if mobile power management did not account for the difference between "blitting array of 2D pixels" and "running massively parallel shader". Even if not done for energy conservation, it might be for TDP profile.

Separately, it's long been a thing on Nvidia Optimus laptops where the most inexplicable thing could cause the iGPU to be swapped out for the power-hungry discrete GPU. A GL-powered terminal definitely seems like it could be in that territory.

In short, many reasons it could be less efficient, hence the question, is there any evidence that it /is/ less efficient?

These days a lot (most ?) of rendering toolkits are GPU accelerated, including things like your browser - you'd likely hit those issues with other apps as well then.

You could hit drivers bugs for sure, but that means in your particular config GL will be worse so you need to test, doubt this translates to a general scenario.

I think a lot of people assume because your default GL setup is to use immediate mode to re-render everything at refresh rate that's the only way to do rendering and that's why GL apps get the reputation for being power hungry.

It may or may not be - it certainly should be tested.