Earlier quoted context omitted.
150k is pretty bad for a senior dev in NYC fyi. Perhaps you have answered your own question. Banks will pay at least 2x more and large tech companies closer to that than what you are offering. Note I'm not talking about truly great developers, merely good senior ones.
I'm not sure I agree, especially when you factor in substantial equity. We have interviewed numerous people from banks and large tech companies and our salaries certainly don't seem out of whack. For reference, $150k is right on target according to AngelList data: https://angel.co/salaries
I only have anecdotal data, I don't think many people have more, but I am very sure a decent senior dev can get way more than what you are offering.
I think there is more to a job than just the salary, but at least be open about the fact that there are open positions doing similar work in the same city offering significantly more.