The 5600G had 7 graphics compute units, the 8500G only has 4; if it performs within 10% of the 5600G, the compute units are almost 60% faster than 3 years ago.
They had better be; 5000G chips are based on old GCN Vega stuff, while these are based on the latest RDNA3 architecture. They're also clocked MUCH higher, as AMD focused a lot on clock speeds when developing RDNA2.
In fact, pretty much all of the performance gain going from a 5700 XT to a 6700 XT is based on the latter's higher clock speed, as their specs are very similar otherwise (although a 6700 XT has 12 GB 192bit memory and a heap of cache, whereas the 5700 XT has 8GB 256bit memory that runs a small bit slower, and crucially, way less cache).
Yeah it's a shame, you really have to step up to the 8700G (or at least the 8600G) to get the true APU experience with modern graphics performance. That said even the bottom of the range significantly outperforms Intel's integrated solutions, and I support anything that gives them a kick in the pants to ship better iGPUs - one step closer to my work laptop being able to run the Windows desktop at 4k without turning into a laggy mess.
At least you hope, it is more power efficient due to advanced manufacturing process. And then a totally disappointment: new CPU consumes significantly more both under load and idle. The AI-extensions are also missing. ECC is missing in all 8300G/8500G/8600G/8700G.
Got a link for the ECC claim? Last I read, the ECC issues with the AM5 platform were mostly fixed (at least many vendors are claiming ECC compatibility again, which they didn't a year ago).
5xxxG are also known for missing official support, only PRO favors have it.
Since ECC is for robustness I'd really prefer when both AMD and ASUS/ASRock/Gigabyte/MSI/... mention ECC support in the specification. Last time I've checked, only ASUS did mention it for consumer AM5 mainboards. (Gigabyte did it for (at least) one simple but expensive server mainboard.) While for AM4 it wasn't such an issue for other manufacturers too.
Yes, the 5700g and 5600g can score lower amount of peak power, but you need to compare the power used against a metric like time to calculate efficiency.
The $179 8500G is competing with the $449 Ryzen 7 7800X3D in efficiency. It's a blood bath.