Remember "Monster Cables"? Everyone had to have car-battery cables to connect their speakers?
Remember when somebody asked "audiophiles" to compare "Monster Cables" and alternatives? Their preferred speaker wire was just a straightened-out metal coat-hanger?
It's extremely easy to tell the difference. I can't tell you what's wrong with their experiment as I don't know exactly what they did, but they clearly fucked it. If you're looking at a static image, you can't differentiate 240Hz from 30Hz. You need a test that actually demonstrates the difference.
I have yet to draw the comparison in person (only have a 165Hz), but I mean, every time you double the FPS, the benefit of doubling them again halves. Going from 120 to 240 to 480 Hz is going from 8 to 4 to 2 ms in terms of frametime.
A 4 ms difference in delay might be somewhat noticeable, if you have a very well running game and amazing reflexes. Anything beyond 240 is marketing bs / e-sport 'I need every ms I can get'.
The benefits don't halve. It's the difference between noticing stroboscopic effects and not noticing them. Between not being able to comfortably track fast moving objects and being able to. 1000Hz is a point at which several limitations of LCD technology become invisible.