A Portable playstation with the same architecture of the PS5 with a slower clock speed would generally only need reduced resolution in order to patch the games. That's not a tall task, especially with most games playing probably at 30fps.
The steamdeck hasn't really changed the calculus on portable gaming. The switch on the other hand has.
The Series S wouldn't have a problem if it didn't lack memory and actually played Series X games purely at lower resolutions.
This hasn't been true for a number of years.
We're now in a world where the GPU is used to accelerate a lot of things in a game that don't scale down linearly with resolution, like the traditional pixel and vertex shaders used to do. GPUs on AAA games nowadays will do procedural generation, physics and fluid simulation, BVH traversal in ray tracing, motion vectors on temporal upscaling, etc. Not to mention the compute-based geometry processing of Nanite in UE5 that is bound to be in AAA games from all the big publishers.
These are tasks that when put together they impose TFLOPs out of the GPU's compute budget and won't go away with a lower resolution.
Sure, the Series S' main issue is indeed the small 10GB pool (or rather a medium-slow 8GB pool paired with a super-slow 2GB pool).
However, Microsoft sold the idea of the Series S as a console that was going to run the exact same games and settings as the Series X but at a third the resolution, from a 4K (upscaled from 1440p) presentation to a 1440p (upscaled from 1080p) presentation.
In reality, that didn't happen. Proof of this are all the Xbox games that have a raytracing mode in the Series X but none of it in the Series S. Or games that have a 60 FPS Performance mode only on the Series X.
No matter how fewer pixels the smaller GPU has to rasterize, all the compute stuff must happen as well because of feature and gameplay parity.
So no, you can't just tell the game engine to target half the resolution and the game will run flawlessly on a GPU with half the compute power as long as it has the same amount of memory available. At the very least you'll need developer intervention to apply more aggressive downgrades to cater to the GPU compute deficit, and/or more than half the compute power on the smaller GPU to compensate for all the non-rasterization compute tasks that take the same amount of compute regardless of resolution.
Imagine if PS6 ends being Vita hybrid
I can't see a portable PS6 releasing in 2028 being more powerful than a PS5, let alone a PS5 Pro.
Unless it has a dock with a discrete GPU using a very fast and wide bus, but that wouldn't come cheap.
