Section 110.28 doesn't define either enclosed or enclosure; Article 100 does. Enclosed and enclosure are both defined in terms of "surrounded" and basically for the same purposes, ( ... prevents persons from accidentally contacting energized parts ...) That sounds like a fair amount of mutual inclusion to me. Most raceways (also defined in terms of enclosed) are not marked with an enclosure Type. Some, like wireways, may be.
I have already expressed my opinion,:"If MC (-HL or not) is not "subject to damage" by nature of its location, I personally see no requirement for auxiliary protection."
The more "wordsmithing" the Code goes through, the more ambiguous it becomes. It's hard enough for the Code Making Panels to coordinate content, it's a monumental task for the Technical Correlating Committee ,hence the need for 90.1(C) and 90.4, first paragraph (although it's a responsibility not a free grant of prerogative).