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.
This is not true in trading. If I go take my strategy/forecast and go to a competitor, I can just outright take the same opportunities that the other desk was taking (to a fairly good approximation). There's no real branding/network effect - it's a pure quality of execution business.
Furthermore the industry attracts the sort of people who are never satisfied with what they got, and are always looking for more.
Not that I'm advocating for non-competes, just saying that you can't address the concerns non-competes are attempting to address by "paying employees well".