Yeah, Kendall Square has definitely filled that nitch for a while. There have been enough successful exits, particularly in biotech, that I don't think it's really any contest as far as the local area goes.
It seemed like the startup scene was going to expand to more of Boston and Cambridge for a while with YC doing one batch of startups there each year but they gave up on that. I was running a startup in Boston for a while and talked with the mayor about his vision to make the old port area a revitalized live-work space for startups but it seems to be happening very slowly if at all. Meanwhile, tons of promising startups keep pouring out of the area and NYC is becoming the #2 US startup hub.