also gfxbench in general isn't that meaningful, for example Gen9 is abnormal fast compared to mobile Vega and in real world Vega trashes Gen9. The ALU 2 score of Adreno 640 is much worse which is a better indicator.
Gen 9 performs in general better because Intel was once in mobile and it became optimized for this. I even saw Cherry Trail doing better than some Iris parts.
Also, if you look Anand's Galaxy S10 and iPad Pro 2018 review, you'll see that the GPUs throttle to about 2/3rds the performance or less.
https://www.anandtech.com/show/14072/the-samsung-galaxy-s10plus-review/10
https://www.anandtech.com/show/13661/the-2018-apple-ipad-pro-11-inch-review/6
GPUs that outperform HD 620 at peak, underperform it when running the bench sustained. Even the iPad drops to 60% of the performance when running GFXBench 3.1 Manhattan for a long time.
The reality is, while the PC vendors(Intel and AMD) execute quite horribly, differences in performance exist mostly because of the greater thermal headroom available on the PC parts. I think even this example shows mobile GPUs in a too optimistic way, because the benchmark, no matter how good it is, can't replace a usable application.
It's simply, impossible to fairly compare the mobile GPUs to the PC ones because of this.
On PCs, we judge harshly the vendors that only show peak performance, because we want to see how it performs after the thermal headroom is used up.
On mobile, its nearly the opposite. Nearly no one cares about sustained. Partly its cause the devices don't need to perform at peak for a long time.