I think you would have to use the field ARTISTSORT to get the right name with or without the "The". "Beatles, The" might be rather straight forward, "The, The" probably is not, groups like "The Head & The Heart" are rather special ...
To get the first character from the ARTISTSORT field, use
and to get all the special ones like 21 Savage use
or perhaps a little sleaker:
A personal note right here:
Even though it is technically possible, I would not do it.
I think that the extra letter plus the folder separation character \ gobbles up valuable space for filenames.
As you have to fill the ARTISTSORT field anyway, it would be enough to get all the Beatles tracks together into one folder "Beatles" (or "Rolling Stones" even, not "The Rolling Stones"). Any player should find the correct artist, it should not be necessary to use the filesystem as major sorting instance.
But as I said: just my personal opinion.