It's semantics. Other major cities all incorporated their suburbs. Some of them are literally 10x+ the "size" of Boston in square miles. On a national scale, Cambridge is Boston, period.
So Cambridge/Brookline/Somerville resisted having their borders officially be part of Boston. BFD. Are they all part of the same heavy rail transit line? (without needing to use the "commuter rail" part) Yes? Boston.
Considering we are talking about a SKYLINE perspective, who gives a crap about voting rights? A 1000' tower in Kendall is a 1000' addition to the "Boston skyline." PERIOD, END OF STORY.