As I mentioned, Samsung killed off its internal ARM core design team. So, future Exynos chips will presumably have off-the-shelf ARM cores + RDNA GPUs.
I don't know how much customization Qualcomm is even doing of the cores in their SoCs, any more. In fact, the only ones still designing their own mobile ARM cores from scratch is Apple. So, it shouldnt be a big loss for Samsung to switch from Qualcomm Snapdragons to using Exynos SoCs with stock ARM cores. I guess the idea behind using RNDA could be more about cost savings vs. Mali, than to gain a huge performance advantage. I'm skeptical of just how well RDNA scales down to ultra-low power. I guess we'll see.
BTW, it'd be crazy if they're actually using HBM2. That could go a long ways towards explaining the performance numbers. I thought it would be embraced for mobile, years ago.