Toshiba 8TB, 7200 RPM
WD Red 10TB, 5400 RPM
Seagate IW 10TB, 7200 RPM
I can see why the Toshiba would generally outperform the WD - higher RPM is overcoming the size difference. The more puzzling aspect is why the Toshiba edged out the IronWolf. Seagate's drive is the same RPM as well as larger. At least according to the specs.
Did you run an acoustic check on the Seagate for primary frequency, or do a rotational latency check, to measure the actual RPM? If the Seagate were at 5900 RPM, the results would make a lot more sense.
btw - this story gives the WD Red as 7200 RPM. But the actual Red review gives it as 5400.