@kjentech I do not use MOC pages and Graph views so perhaps I do not understand correctly. But could not this be solved by logical AND,NOT,OR operators?
Something like:
("" -tag:#moc) OR ("" file:MOC-Index)
Empty string in paired double-quotes matches any file just like in search-bar in Windows File Explorer. Replace it by your search string where appropriate.
I intend to use “+” sign for adding filter/search terms/conditions that do not clutter matched results: Global search: Non-capturing match = Filter by textual context