Either there is something magical about that 4K TN panel, the IPS is calibrated appallingly, or your eyesight isn't what it should be, because I do not believe anyone with fully functional vision couldn't see the very obvious difference between TN and IPS... it's night vs day. Whether this bothers you or not is another matter and entirely subjective however.
Thing is - it used to be you'd sit a TN beside a good IPS and it would be horrific the TN would stick out like a sore thumb - but recent "10bit" 4K panels and the TN Swift, etc. when calibrated are largely inoffensive when sat beside an IPS panel - sure there will potentially be issues with gamma shift/viewing angles and don't have as deep and detailed colour saturation but they aren't a million miles off in terms of colour accuracy, saturation and overall image quality.
There is a huge difference having my old XL2420 beside my U2913wm while the Swift is being RMA'd compared to how the Swift looked beside it.
Looks like a dead pixel and a thunderbug...but if that's a thunderbug then the monitor has been used...
They're attracted by the light. So it would have had to be powered on.They've appeared in XB270Hu and PG279Q unopened ones aswell, so not necessarily.
You able to check what gamma its at out of the box after OSD-only calibration?
And is top noticable darker than bottom, does bottom look washed out?
Brightness you mean?, i think it was 75, i've got it at 11 now.
Bottom looks fine in person.