Most quant strategies aren't really dependent on insanely fast execution. They may hold a position for weeks or months at a time.
But regardless, HFT usually means latency arb, not just trading a lot. There's a misperception that quant funds are making money on slight mispricings, but while I can't speak for all funds of course, this isn't generally true. Quant funds are much closer to buy and hold long term investors than they are to HFT firms.
They aren't measuring the market / order book and then reacting at high frequency. They are reacting at low frequency and then the execution is optimized to minimize losses caused by market feedback.
This is a very important distinction if you hold the view that HFT risks destabilizing markets.