The two main issues I have with them are that firms tend to give them to just about everybody (instead of just to folks working very directly with real IP), and they only pay base salary, not something closer to actual total compensation (often multiples of the base pay).
Having said that, the quant firm is relatively unimportant and not a good reason to prevent a total noncompete law. It's probably better to just ban them then try and make allowances that aren't full of loopholes.
So the solution is that employees should only be able to work for one employer in their career? I wouldn't disagree with this argument if the noncompete came with a payout in the tens of millions of dollars.
That's just employment, so its effectively the status quo in places with a ban on noncompetes. You can absolutely hire someone as an employee, when their only job duty is not to compete with you. You can even contract such employment for a set term. The problem, of course, is that employers want noncompensated noncompetes and at-will, no-set-term employment.