Jeremy, you are right!
And yes, when i choose “share” (Master File Default) from FCPX, the resulting file is very different from the original: sometimes the quality of the image is either worse (Like the web publishing mode), or the file takes up too much space. I do not know why this is so.
For this reason, I use Compressor, because I can adjust the quality/bitrate correctly. In FCPX export settings I do not see such possibilities.
Maybe I missed something?