I'm confused about your post, and not just because it's a wall of unbroken text.
Initially scanning to create your library has nothing do with tagging. If your library is 400CDs ripped to wav and was previously accessible in another program, are these files not tagged or denoted as to what they are in any way? Musicbee should be able to read the existing tags (or cue sheets) and get some sense of what's there without auto-tagging at all.
Even if they're not tagged, but are named something predictable like Artist - TrackNo - Title, MB should be able to figure out what they are. Unless your library is a mass of files that are not identified in any way, auto-tagging is like step 2 or 3 in creating a library, not step one.
Are they individual songs files, or one file per CD with a cue sheet?
That said, if you're dissatisfied with the results tagging through MB, my advice would be to tag your files directly in MusicBrainz Picard, which works quite well at scanning and identifying through sound signature, before trying to import them into MB. Don't know if it works with cue sheets, so if that's the case with your library it may or may not be an option.
Some of us have been working for years on building and correctly tagging our collections, so complaining that it might take you hours to do this is not going to gain you the sympathy you think it will.
Even working perfectly, yes, it will take you hours.
And there is no "support" to work with. The program is developed by one man, and "support" is this group of enthusiasts you've found.