I tested the new settings in 5.2.0 beta 1 — but only combinations of “Folder” and/or “MB ID”:
Seems to be working very well, I tried various settings even with mixed tags (some albums having MB IDs, some not. Some having " - CDx" suffixes in the Album Title, some not).
All combinations worked nicely, I could not get any “weird” looking results. Just checking “MB ID” seems to use the Album Title (“ALBUM” tag) for grouping anyways, because even albums without MB IDs are grouped perfectly fine according to their title.
So for me this is a huge improvement.