Reacting faster than others to markets is not front running. Seeing someone else's order and putting yours in front of it is front running. Traders on the NYSE Floor would hear a big order is coming in, and put their ticket in front of it- that is front running.

In a computerized world, front running has essentially ceased to exist- the last major enforcement actions I could find are from 2003, when there was still quite a bit of trading done not by pushing buttons on a computer but by making phone calls. Trading on inside information is alive and well, but this is not what JS does at all, that's the realm of hedge funds that have traders that still click on buttons.

I never worked at JS, but have worked in MM.