I've been experiencing this for a while now, and been doing various tests, all of which unsuccessful. The final product on YouTube isn't as sharp as the original ProRes, or h264 as I've tried both, and it's also darker/slightly de-saturated in comparison to the original file.
Is there something I'm missing out along the way to cause this?
I usually shoot in ProRes HQ - Film - 25FPS. From there, I edit it together in FCP (currently 7 as I'm more used to that), colour it in Resolve and then add final layers back in FCP 7. That get's me the ProRes Master file, and if I need a h264, I'll put the master file in FCP X, and export accordingly as it's a lot quicker to compress.
It still all seems a little darker to me, and I can't work out why. Should I brighten everything in the grade to balance it out?