"The numbers paint a transformative picture my eyeball tests immediately confirm. Stick both sets in Vivid mode, and the resulting 1,361 nits of the G3 compared to the 800 nits of the C2 is truly game-changing. Considering this year’s LG C3 OLED is more or less a match for the C2 when it comes to HDR brightness, it makes the LG G3 the undisputed king of the South Korean firm’s OLED line-up."
I did the same tests with the LG 77 C9 and with Vivid mode and some standard HD I could see a little more brightness but in HDR and Dolby Vision shows it was rare to see any differences. I had them side by side and most of the time when I thought the G3 was brighter I just had pause the video and look back and forth a bit to find that they looked the same. Because of the differences in C9 and G3 color temperature settings the C9 would even look brighter in some parts. The only real example I could find in a UHD 4k Blu-ray was the newer DreamWorks intro for the Puss in boots the Last Wish, when the crescent moon is floating around it is brighter on the G3 but that was about it. Even in bright daylight scenes they just looked the same as the HDR info was never asking for more that either set could handle.
In addition I got one of the G3s that makes pops and snap sounds randomly the whole time it's on, now after a few months. Mostly I wish I had just kept the C9. I just got taken in by all the talk over the years that the OLEDs are not bright enough for bright rooms and so on. If you want to use Vivid mode that changes a bit more than just the brightness or feal you need brighter standard HD it may be worth it but if you feel like you are missing out on more detail in HDR or Dolby Vision with more color accurate settings than Vivid, I don't think you are. Again, with the same 4k UHD Blu-ray side by side it's real struggle to see any deference between the C9 and G3.
It may just be a YMMV situation, went from 55 C1 to a 55 G3 and there is a big difference to me, also have a 55 G2 available that I rarely use now because I love the extra pop it gives(and the misses took over the room it is in helping to "justify" the G3 purchase in the first place). My comparison isn't apples to apples because I did not like using vivid on either the C1 or G2 but something about how vivid with some tweeks looks on the G3 just really does it for me. My totally unscientific brain thinks maybe the extra brightness makes everything still look good without looking overblown and washed out in vivid like the older sets did.