FWIW, I now upload video to YouTube using “lossless H264”. On the codec tab change GOP to 30 (i.e. 1/2 frame rate) and BFrames to 2 as per the YouTube recommendations.
https://support.google.com/youtube/answer/1722171
I don’t see the point of getting Shotcut/ffmpeg to munge your video when YouTube is going to re-encode anyway. File size should be roughly the same as source files provided not a bunch of filters on the input video.