Has anyone here ever actually had complete success with Encore, from project inception to working blu-ray disc?
Yes. It may not be amazing software, but Adobe did not ship a product that fails to build discs.
Now, the potentially foolish thing on my part was attempting to put an m2ts file on a Standard DVD, which for all I know may be impossible to do, but from what I’ve seen, Encore can down-convert high-def files. In further researching the issue, I came across this forum:
First of all, certainly do switch to blu-ray mode instead of DVD, if that’s what you intend to build. The compatibility with codecs will be different. I.e., if you want to import and use an h264 file, that will be compatible with BD but need to be transcoded for DVD. Secondly, everyone commenting in that link you gave says to demux the m2ts or mkv into individual streams with tsmuxer (this is something I also mentioned). It should work fine.