AMD is probably wary of making a "super APU" outside of what they sell to the console manufacturers, for various reasons.
The high-end desktop APUs we do see are just the TDP-up-up versions of the laptop APUs. The 65W TDP Ryzen 7 5700G probably uses the less efficient dies that would otherwise become the Ryzen 7 5800H or Ryzen 7 5800U in laptops. AMD relaxes the TDP limit, boosts the clocks, and OEMs can add it in cheap desktops with lower quality cooling, lower-wattage power supply, and no discrete GPU.
If you look at next year's "Rembrandt" successor to the 8-core 5700G, it will probably have 75-100% more graphics performance due to an increase to 12 RDNA 2 CUs, instead of 8 RDNA 2 CUs in the Steam Deck or 8 Vega CUs in the 5700G. It will deliver decent 1080p gaming performance. According to Steam, 84.75% of players are at a display resolution of 1920x1080 or lower. Forget 4K gaming, even 1440p is irrelevant at the moment. It will be sold in complete OEM systems for around $600. Add another $100 for a cheap monitor or TV, and maybe $50 for peripherals. So a $750 gaming setup. A 6-core version could be cheaper.
A Rembrandt desktop APU should actually be around the performance of the Xbox Series S. The CPU will be better, so no worries there. Xbox Series S has 20 CUs at 1.565 GHz for about 4 teraflops (RDNA 2). Rembrandt will have 12 CUs. I doubt it will run at 2.6 GHz, although maybe it can when overclocked. Then there's memory bandwidth. The Xbox Series S uses GDDR6 for 224 GB/s for 8 GB, and only 56 GB/s for the remaining 2 GB. Rembrandt should support DDR5-5200 and can use larger amounts.
In the future, we will see more exciting APUs. They could stack gigabytes of memory on or near the chip to increase performance. But even without that, each new iteration of laptop APUs will raise the bar for low-end gaming.
My understanding is that FSR is less effective at lower resolutions like 720p and 1080p, because there are less pixels in the first place for the algorithm to work with. So the Steam Deck using FSR to upscale to 1280x720/1280x800 might not make much sense. FSR is pretty good at turning 1440p into 4K (maybe that says something about the necessity of 4K). That said, FSR 1.0 is just the beginning, new versions are coming soon, and RDNA 3 may have specific hardware acceleration for FSR, so 2023+ AMD APUs with RDNA 3 graphics could benefit even more. Intel/Nvidia graphics can also benefit from FSR.