Since this is but an iPhone crammed into a laptop, could this behaviour stem from the fact that iPhones generally need not render a cursor?
EDIT: Also note that there is nothing new with the Neo here, as all Macs since the M1 have used the same chip architecture as the iPhone.
Desktop GPU designs did not focus on tiny efficiency gains, and often only has a primary plane, a single overlay plane (for e.g., a video), and a dedicated cursor plane. Some even have to share a single overlay plane between all connected displays. It's a recent thing for desktop GPUs to get more flexible in this area, in part to improve laptop battery life in the cases where the laptop is almost entirely idle.
(For those unaware, a "plane" here is the entity in the display controller you configure to show a rendered graphics buffer, in a particular location and with particular transforms. You commonly have one plane that just covers the whole screen, and then sometimes put dynamic content on top in other planes so you can avoid having to redraw the main buffer when smaller bits of it change, like a video player or cursor. You could also e.g., scroll by rendering an entire document in advance and then move the plane around to reveal parts of it.)
I'm not sure they're all that tiny if you can squeeze out 70% of top end performance for 25% of the power draw :)
#1 (by far) "can it play [hot game of the moment] in 4K?"
#2 (maybe) "is the fan noisy in desktop mode?"
#3 (for nerds) "can I run LLMs on it?"
I don't think top efficiency in desktop mode is on anyone's list, and even if it were, it would be hard to come up with a design that uses hundreds of watts when running top-tier games or LLMs, but also uses as little as possible when idle?
Very different metrics - the former is about optimizing your architecture for pushing the most operations, the latter is about being able to power as many things off as possible.
Peak performance happens at peak power draw and is a matter of having as much hardware as possible pushing as many operations as possible at any given point without spontaneously combusting. Those who have the most advanced manufacturing process, or architecture with the most execution units and best able to keep all units busy wins.
Peak power efficiency is about being able to turn as much hardware off as possible, and having lower quiescent current ("leakage power"), with bigger, beefier chips naturally having higher quiescent currents.
What is talked about here is about gating hardware such that you can shave off milliwatts or microwatts when the system is completely idle, by taking tasks that otherwise use slightly larger blocks that would have to remain on and moving them to smaller, more dedicated blocks. For example, being able to play a video with most render capabilities powered down because the display server can take the output of a hardware video decoder block and feed it straight into a display controller plane.
Nvidia (and AMD and Intel) just suck at efficiency. There is no excuse for such a performance-per-watt delta. The same is true in CPU land.
Once the first ARM Steam Deck launches gamers will realize they've been had for a decade.
Also not sure why you'd label it as "M0", as trivially beats the M1 on several metrics.