Yes. It is not a bug. See also
It appears that, in your case, there is not much processing and only decoding. Shotcut still decodes on the CPU, and that becomes a bottleneck for the encoding. It does not make sense to do hardware-accelerated decoding if all of your processing and effects are not using the GPU. Making everything run on the GPU can be a goal, but it is extremely difficult to do cross-platform and cross-vendor. That is why some companies’ software only supports NVIDIA CUDA for GPU for example. Shotcut is not going that way.
See also FAQ