The same is true for a 1:1 pixel ratio. So this doesn't count as an argument for the 2:1 ratio.

With all due respect, I believe that's a made-up argument that one of your tech guys mentioned as a joke during lunch while the PR guy he was sharing his lunch with thought it would make for a great "tech-sounding" excuse.

Of course, more pixels will need more computation power, and hence, produce more heat. That's basic thermodynamics.
But unless you intend to decode videos in software I would assume, that the effect whether the GPU has to compute 1 million pixels or 260000 pixels is negligible.
I would even claim, you can't even measure the difference, because the effect is dwarfed by measuring inaccuracies of your thermometers and fluctuations in ambient temperatures. If I'm wrong and you can do that, I'd like to see the data.

I think it's much more likely, that you tried Gnome (and probably KDE) at the native resolution and saw that all the controls are too small for fingers.
Then you looked for an easy way to scale the controls up without making the rest look ugly. You found Gnome's scaling option and saw that it produced nice-looking results.
This was probably the point where you decided to anounce that you'd rather go with Gnome instead of KDE.

It's the path of least resistance and I don't blame you for going it. But please, cut the PR crap!