That would only happen if fintech didn't change their behavior in response to such a tax. I do not find that to be a reasonable assumption.
Your claim is of a piece with claims that raising the minimum wage would destroy jobs, and people on minimum wage would be out of work. Guess what, we tried it anyway, jobs didn't vanish at all, poor people have more money to spend on necessities, and everyone is better off.
US Financial Sector profits: $422 billion
>It would still be worth conducting fintechy business. It would barely affect bonuses.
It is absurd and blatantly false to claim the entire burden of the U.S. healthcare system could be placed on a single industry with little effect.