The method shown in that youTube video is the only way in NXT 5 to createa DVD without a menu. The myDVD in NXT 5 is useless when you want to do any custom menus etc.
Now as to quality of the DVD. I have no idea what quality your selected for your DVD. First of all if your source videos are HiDef (mts, mp4, etc) then the quality on the DVD will be quite a bit lower, after all the video on the DVD is "standard" 720x480 video. Also file size of your source videos is basically irrelevant, it is the time length of the video that matters. A standard 4.7GB DVD can only hold 60 minutes of video. Any longer the bit rate has to be reduced and you lose quality.
If you can re-install C2012 then that is what I would do