WOW, just like you said, something is badly wrong. As you can see here
http://www.anandtech.com/show/8407/ocz-arc-100-240gb-review/5 everything sequential shoudl have hugely better performance.
Get on latest firmware "...ARC 100 1.01 Jan 29, 2015 Mandatory Update Release Notes
IMPORTANT: This is a mandatory update for system stability. OCZ urges all customers to update to 1.01 as soon as possible to ensure the continued reliability of their drives....." If you you were hitting read errors then that would explain the low rates. Samsung had problems with programming their flash that lead to read errors. I wonder what the firware update changes for the ARC 100. (I don't follow bigfoot controllers so don't know).
2. Do you have a tool that can pull the SMART data from this drive? Or does the OCZ toolbox give you smart data? If read performance is still bad after firmware update then suggest you look at smart data for anything that looks like error counts or sata downshift.
This page gives Smart data descriptions. click " Indilinx" for your bigfoot based controller.
https://code.google.com/p/hddguardian/wiki/Indilinx_SMART_attributes you can look at some of the other drives for more information on the standard SMART data definitions. Or google it.
Please let us know what happens.