So, hypothesis, OLED phones, monitors and TVs with DC dimming still have a flicker, a "brightness dip" that directly corresponds to their refresh rate, lowering the refresh rate will reduce the overall amount of times the device flickers, therefore improving the viewing experience on static images or lower framerate video where you don't benefit from monitor refresh rate motion clarity.
(Do note that this brightness dip is OLED exclusive, it is not present on LCD monitors, if you see any difference on LCD, it could be due to a gamma shift that occurs in some LCD monitors)
In practice? Yes, at least for me, lowering my 240hz OLED monitor to 60hz, does make text easier to look at and I've confirmed this with at least 2 other people, with a "blind test".
Additionally, I've also tested 1920hz vs 60hz DC flickering on a Poco F5, by changing the brightness threshold ever so slightly to change between the 2 modes and the DC dimming was more comfortable.
So, perhaps in the end, this means that chasing OLED phones or devices with high hz dimming isn't actually a good idea, as it's the amount of flicker that matters and not just hz? As seen in this example, it's 60hz vs 240hz flickering, where "60hz" ended up being better, same with 1920hz vs 60hz.