You have 3 different disk sizes, parity check can never be faster than the slowest disk at any point, and disks are much slower as they get to the inner cylinders, so it will slow down 3 times, especially noticeable as it gets near the end of the 3TB disks, then 4TB and finally 8TB.
Also you have some disks that max out at around 150MB, even on the outer cylinders, like the 4TB Reds, so 130MB/s is not bad, it should be more than that in the beginning but there will be points that it will be much slower, you can get an idea by running the diskspeed docker.
Hardware wise your fine, just make sure the HBA is on one of the top 2 slots, the x8 CPU slots, can't see that in the diags.