That graph matches with my experiences over here in Paraguay, South America. Between 500GByte and 1TByte Seagate drives are really bad, anything between 1 and 3 TByte is bad as well. However, the 500GByte, the 1 TByte and 3 TByte models perform well. Over here it is so bad that I don't even want a Seagate drive with an even number for storage capacity, even if you gave me the drive + money for free. The headache, misery and loss of time just isn't worth it.
Unfortunately, Seagate (and Samsung, if you count portable drives) is the only brand you can buy here directly. All other brands one needs to be ordered online and the extra shipping costs are prohibitive.