This is true, but FPGAs can still only handle relatively simple algorithms. FPGAs make certain kinds of tasks nearly trivial (think truly parallel tasks such as decoding market data for different instruments), but there's just not enough gates (in most cases) to do interesting stuff in the application / logic layer.

FPGAs canonical use case is still as very fast codecs. There are exceptions, but they're really only the very simplest of arbitrage strategies. And in order to make those work you need top-of-the-line network gear and engineers as well.