1.
The
amc script renames files solely based on ID3 tag information. These tags are not guaranteed to be correct or uniform. You can however modify your custom format to maybe normalize things to some degree.

You may find simple
filebot -rename calls more effective for dealing with custom use cases such as this one. You may prefer to use
--db AcoustID to normalize naming based on AcoustID metadata.
2.
--conflict auto is designed for comparing video files by quality. It'll probably default to
"bigger file size is better" if we don't have any video characteristics to compare. Note that
--conflict auto refers to file paths conflicts
(i.e. can't have 2 files with the same file path) but not logical duplicates
(i.e. have 2 different files with 2 different file paths that happen to be the same song).
3.
The
duplicates script only works for logical duplicates based on
xattr metadata which means that it only works for
Movie and
Episode type files that have already been processed and identified by FileBot, and thus doesn't work for music files at all:
viewtopic.php?p=23171#p23171
4.
FileBot can work well for renaming / moving music files due to it's flexible naming scheme and programmability, but if you need more of a music library management tool, then others tools might work better for you:
https://beets.io/