I had to read the thread twice to understand what was happening.
If I may, I will clarify what RD said:
That does seem like a bug if it's not reading the APEv2 ALBUMARTIST tags from the MPC files and saving them into the MC [Album Artist] tag.
And that is exactly the case, when I looked at your two sample files. MC isn't reading the ALBUMARTIST tag from the MPC file, as shown by the [Album Artist] tag being empty in MC after the files are imported.
The MP3 file does have the "Various Artists" value in the [Album Artist] tag of course.
But then I see another issue to resolve. You still have the original Album name in the [Album] field for each track. So MC is going to consider them from two separate Albums, and not combine them into a single Compilation Album. What I do with compilations I create myself is change the [Album] field to a value I assign for the compilation, such as "Compilation - Hard Rock". MC will then treat all included tracks as belonging to the same Album, and [Album Artist (auto)] will work correctly. The downside is that you lose visibility of the source Album in the Compilation Album. Maybe someone has a suggestion on how to get around that. I don't worry about it. Of course if we are talking about a commercial compilation, all Tracks should already have the same value in the [Album] tag, so this wouldn't be an issue.
If you make the above change to the [Album] tag, I would then do as RD says, replace that expression for Album Artist with just the tag, [Album Artist (auto)], then delete the contents of the [Album Artist] tag in MC. MC will then assign "(Multiple Artists)" to [Album Artist (auto)] as intended.
If you don't like that, you could then add back in "Various Artists" to the [Album Artist] tag for all Tracks, and that will show up in the [Album Artist (auto)] tag. Note that when you do that in MC, the original APEv2 ALBUMARTIST tag in the MPC file isn't deleted or overwritten, but a new APEv2 tag called "Album Artist" is written to the MCP file. Once again confirming that MC isn't using the APEv2 ALBUMARTIST tag for MPC files.
BTW, I assume that these compilation albums are actually based on separate copies of the included tracks, and that they are all stored in the same sub-directory together. Otherwise, the above issues get far muddier.