I can melt my sn62pb36ag2 (should liquify at 180C) with the iron set to 190C, so that's pretty good, I'd say. But when I measure the tip temperature with the tip tester or the DMM, the discrepancy increases the higher the temperature gets. Set temp 350C = 318C tip thermometer / 295C DMM, that's very far off.
Fluke rates their thermocouple to 250C, but from what I understand it should work fine at higher temperatures. At room temperature the tip tester and the DMM agree on the ambient temperature, but it's hard to test both equally well on an iron tip. I can imagine the ~20C discrepancy between them is because of the large thermal mass of the DMM thermocouple and the different ways of pressing them on the tip.
I know there's different PCB revisions, many different firmware releases, different tips and defective tips. 270C vs 300C and 318C vs 350C is a pretty massive temperature differential right inside the typical working range of a soldering iron. I guess my hardware might have a defect, but then again that video I linked shows the exact same problem, so maybe it's just a certain PCB revisions that's performing poorly. Or both my DMM & tip thermometer are inaccurate.