Are you viewing your video on YouTube at only 360p? don’t forget to change the qualtiy to 720p! If that is really how youtube is displaying even at 1080p, then try exporting your video to mp4 (internet HD 1080p preset) and then select customize tempalte, and then go in there and first make sure your frame rate matches the source, then change the profile from “main” to “high” and then go down to your bit-rate and change the maximum bps to 14,000,000 and the minimum to 11,000,000.
Then render than and upload it and see if the quality has improved. if it still hasn’t, then this is likely a youtube issue and I would message them and tell them that they need to improve the way they transcode video.