I'm sympathetic to the idea of more low-income housing, but you're just impotently raging about income inequality here. A prime piece of property in the middle of Back Bay, with significant design challenges, is not going to get developed into low-income housing. Nor should it. Besides, even if this building were 100% low-income housing it wouldn't even make a dent in the larger housing shortage.
Instead you should be advocating for large-scale developments built around public transit further out of the city. We need to be building densely around our already-existing infrastructure in places that are cheaper than a tiny plot in the middle of Back Bay. Only then will we be able to build enough units to actually make a difference in our housing supply.