Like I said, I wasn't sure you were arguing for an exclusively market-based approach, so I edited my comment preemptively. But plenty of people here do that - and do it in a very obnoxious, condescending way (such as "you don't believe in economics") - so I left it up.
If you want to say that keeping things from getting worse is the same as making them better, you can make an argument for that (at least in the abstract). But we're talking about one development so it's meaningless to almost everyone who is being pushed out of the Boston area. What we're really talking about is things getting worse less quickly. If someone is being priced out of the Boston area they're still being priced out either way; they're already facing their worst outcome.
You wrote: "How can you say that economic forces can't be used to address a problem of economic forces?"
I didn't say that. Read again, but carefully this time. I was talking about the idea that market forces alone can solve the problem.
As to specifics, I agree with expanding public housing, as long as the areas into which it is expanded are conducive to a decent life (i.e., a reasonable commute), and it's mixed in with higher income housing. Do anything else and we perpetuate the economic and racial segregation we currently have. That's nowhere near enough, though. We need things like density bonuses for developers, massive subsidies (ideally including federal money) for both the builders and the renters and buyers of housing, a higher mandated rate for affordable units in market-price buildings, and taxes to discourage flipping already constructed housing.
Regarding your last paragraph, we should stop subsidizing prospective corporate move-ins like GE And Amazon altogether. Boston has a housing crisis, not a jobs crisis.