Here comes the tricky part: "finding it first" may imply you're have more and more false positives as you speed things up beyond crazy. And so, even if you have a "deterministic" model (and no, it's neither "pretty simple" nor "proven mathematical" most of time), it will get fuzzier and fuzzier. Also, HFT is execution-centric, indeed, but it doesn't mean you can't use complicated math models and all that, it's just much harder to do and is more of a computational challenge (which is part of what makes it fun).

Source: hft quant