I asked one of the staff what happened to send Persian Art and Culture into a nosedive about that time and why there was so little after that time. She was evasive as any good government bureaucrat but finally admitted that time was a time of great warfare. I knew not to ask what brought on that warfare because I knew it was a time of forced conversion to Islam and replacement of the tolerant Zorastian religion with a religion of intolerance and political oppression.
The flourishing of Persian culture after that time coincided with periods when secularization forced relaxation of the iron grip of Islam, the most recent example being from the early 1930's until 1979.
I saw Persian reliefs at the British Museum that were the
equal of Greek and Roman ones.However,I agree with the posts
about the Arab Muslims co-opting other groups works.