I heard this a couple time. Is there an article or something that demonstrates this? I went looking and everything I find that did GPU specific benchmarks tend to end similar to this...
The problem with direct ATV comparisons, is that there isn't really much interest in the Apple TVs, especially for gaming. So, that means there isn't much interest in doing side by side comparisons, so to compare the performance difference in the chips for benchmarks, you have to use other devices that have those chips.
If you look at the Geekbench 5 Metal test results, the A10X is 30% higher over the A12 for the GPU:
browser.geekbench.com
Now, that doesn't necessarily mean that the A10X is always faster than the A12, as if there is SW that is better optimized for the A12 than the A10X, the results would probably not be too dramatically different.
That said, I have seen posts on MR forum from game developers saying that the A12 is significantly slower for graphics than the A10X in real world testing. This posts could have been faked of course, but when we lack any actually data showing one way or another, we can only take people at their word.
There has also been a posts of people complaining about gaming performance on the new ATV4K2 with the A12 on some Apple Arcade games, including slowdowns and framerate drops during fast action games, such as Asphalt 8+. These issues are not present with the older ATV4K1 with the A10X.
Again, not really a scientific test, though.
There is a YouTube channel that is all about gaming on Apple devices. MrMacRight:
Official MrMacRight YouTube Channel - The best place to find Mac, iPhone, iPad and Apple TV Games! Inquires - mrmacrightmail [at] gmail [dot] com Tech suppor...
www.youtube.com
This guy is one of the few people out there that does pretty good gaming reviews on all Apple devices, including the ATVs. He also compares game performance on AS Macs vs Intels, native games, as well as emulated, Rosetta, Crossover, and Parallels.
When the ATV4K2 was launched, he posted a video showing the actual fps of some of the tvOS gamings running on the A12. He said if the video was popular, he was going to do a full comparison between the ATV4, ATV4K1, and ATV4K2, but sadly, he only got a fraction of views on that video that he does with his others, so it looks like he is not going to do the comparison.
During that video and some other newer ones, he did make a few comments basically saying that he see no improvement of the A12 over the A10X, and a few, I think Oceanhorn 2, there was a decrease in performance when there was a lot of enemies on the screen.
Both seem to be consistently better than the A8 in the ATV4.
The guys at Max Tech said that they were going to do a comparison between the A10X and A12 in the ATVs if there was interest, but sadly, it looks like it still hasn't happened.