It would help if you posted detailed hardware, OS version, pool layout, etc.
You can expand my Details for an example or read the Joes Rules for Asking for Help link in an above post.
We usually start with that and do a network test like iPerf3 to rule out that and then start looking at what you are doing. Please be as detailed as possible on your problem and how you are testing. We the details on your hardware and pool setups we can get an idea of what to expect for performance.
Adding link. I don’t know about the controller you listed but might be covered by this.