Is Radeon ProRender slow in Viewport/Preview in general?

In the advertisements, Radeon ProRender boasts that it is fast. But in Blender’s Viewport (Rendered) it is not very responsive. It is slower than Cycles, and it randomly becomes black.

In my case, the CPU is faster than the GPU and it seems that using GPU makes Blender’s UI stutter, so I use CPU rendering. When using Cycles, if I set a sample like 4~16 for the Viewport, dragging the Viewport is rather smooth. I mean, right after I started dragging the image is jaggy, but Blender’s UI itself responds smoothly. When using ProRender, even if I set the lowest sample count, which seems to be 16, it is still not as responsive as Cycles. Also, when selecting an object, 1 out of 3 times, some part of the Viewport becomes black.

Does this happen to most users, or is this because my CPU is slow?

Feels faster on my side w/ GTX 1070
and much faster – instantaneous using Hybrid mode

When you are not using the Hybrid mode (which I think you mean using both the CPU and GPU), did you use only the GTX 1070 or the CPU? If it is the latter, may I ask what your CPU is?

it is faster on my GPU than CPU (my cpu is a dual xeon six core) and my GPUs re GTX 1070Ti or AMD RX 5700 XT.

Render speed is compared to CUDA not faster it seems to me.
While close the biggest issue is the start time for the first rendering to even start. This can take with the AMD test file up to 30 seconds.

It also is prone to in windows lock up the screen UI - crash/freeze Blender or on macOS lock up the computer

PRP is to me very interesting but it seems they oversell it a little.

It is pretty new so I assume it just might take some time.

Hybrid runs only by using GPU, can’t use it with CPU
(if CPU is set, it auto-switches to GPU when switching mode to Hybrid)
so only Full option is available for CPU,
which in my case is TR 1950X @ base clock (3400 - 4000 MHz) w/ 64GB RAM @ 3200 MHz