The 85% is more than three times better a planet than the 61%, if I recall correctly. I think (quality - 50) * (other stuff) was the factor quality played in that equation, so 61-50 = 11 vs 85-50 = 35.
Also, you get severe penalties with higher difficulty levels. I don't know what very hard's modifiers are, but you're going to be well behind even if the planet wasn't crap to start with. At extreme, I think you get half the normal and they get double, because for similar planets the AI will get four times the GDP than I do out of them. Just a rough guess based on the numbers you showed, but they might get around 2.5 times the GDP per planet than you would due to the difficulty level, were all else equal. So the only reason they are only 7 times ahead of you there is because of your higher population... And because the planet has a low quality, you are going to have a lower top population for the same world sizes.
I tend to avoid planets below 70% unless I'm trying to claim territory with them, or they have some other benefit.