Good post.
By your criteria, what keeps Boston out of that tier?
i guess i would ask what does boston provide that the aforementioned cities do not? it excels in higher education, yes, but so does the other cities. i think what makes the other cities world class is that they are consistently exceptional across a number of different areas.
boston is obviously a great city so don't want to detract from it, but similarly, it's why memphis wouldn't get a nod. yes, memphis has a trailblazing music legacy but so does los angeles (pop, rock) and new york (hip hop). not even mentioning chicago, because i see chicago's musical legacy as a continuation of memphis' - but obviously chicago excels here as well.
even moreso in the classical arena where its second to nyc. and depending on who you ask, some would place classical as more "worldly" than blues, gospel, and even, sometimes jazz. but even if we could agree that jazz transfers as worldly, new orleans, chicago, and nyc have a premium on that before memphis.
nyc/la/chi as regional hubs excel in finance, law, real estate, medicine, tech, education, *design/infrastructure/city planning, history, music, diversity, culture, politics, etc....
for me world class denotes consistent exceptionalism across all of these factors. yes other cities may do well or even better in a few of these areas, however, they don't have the range to score consistently high across multiple areas.