Well, mesa does not do anything regarding video performance. Only 3d performance. Which is pretty good on the RockPro64/Pinebook Pro with the Panfrost driver.
Low video performance, is because of the userspace applications.
The rk3399 SoC, which is used in the RockPro64, uses Hantro/Rkvdec as it’s VPU driver. These drivers are present in the kernel. But the userspace applications, like ffmpeg, firefox, mpv etc, does not support the API (v4l2-requests) yet. The reason for this, is that while the driver is in the kernel, it’s in the staging part of the kernel, which means it’s not been deemed stable enough. That’s why the userspace applications have not made an effort to support it yet.
I’m pretty sure, that once the driver gets out of staging, the userspace applications will quickly add the support and video will be pretty fluent on the RockPro64.
Right now, all video is software decoded.