Yes, but Kraft, like all team owners in Boston, has privately funded his projects, as he will privately fund this one. The question is the extent to which he's required to offset the impacts his projects have on public transportation assets and other infrastructure. At the end of the day, it is the purpose of taxes to support infrastructure that serves the people, businesses, and property owners of Massachusetts, Boston, Everett, etc, and Kraft is a business owner and a landowner who (theoretically I know) pays taxes on his income and his businesses' income. There is a material difference between a billion-dollar subsidy appropriated directly from residents' unclaimed private property (as is absurdly happening in Ohio) and the potential for a busier Sullivan Square and Orange Line station (both of which the City of Boston is actively trying to make denser and busier as a policy objective).
Let's not pretend that the Mayor is an honest broker here - she's trying to (legally) extort him and he made it worse on himself by letting the corrupt soon-to-be-former Mayor of Everett crow and clown on her and then paying for a ton of dog whistle attack ads in an effort to buy the Mayor's office for his Mediocre White Man of a son. He has played this very stupidly (which we might recall is his custom in stadium negotiations), and he has lost a lot of face.
Personally, I believe that since he has functionally infinite money and seems to have nothing better to spend it on than box seats for Wagner at the Trump-Kennedy Memorial Hall, it's fine for Boston to stick him up for however much they can get. That's business and, given the players, perfectly moral. But I don't think it's the same thing as what's happening in Kansas or DC.