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.
Some places won’t compensate for the noncompete at all, others won’t compensate if the person works at a non-competitor. Some have a mix, eg up to a year of (paid) garden leave followed by up to a year of (unpaid) noncompete. If someone does leave one firm for another, there is often some negotiation, eg maybe the hiring firm agrees not to have the person work on certain things for some amount of time (potentially longer than the noncompete) and in return they can get them sooner.
So one solution is to allow noncompetes so long as employees are fairly compensated. It seems hard to discuss improving the rules around fairness there if you’re a politician because quant firm employees are not very sympathetic – it looks bad to say they are mistreated when they make many times more than lots of other professionals, even though by allowing that mistreatment you’re effectively giving the money to their even-better-off bosses instead.
Some would use that money and time to start a competing company :)