The staff at these stations know when people are jumping the turnstiles and evading fares. They know if there is a fight. It’s already recorded on classic CCTV (though with shockingly bad cameras if we are to believe recent news reports).
The issue is not in my mind the detection of crime (especially petty crime). This may or may not improve the detection of crime, with a cost to civil liberties and loads of false positives.
I don’t know if increasing detection of more minor crime is useful if there is not a clear way of being able to respond to the volumes of crime we already know about.
You can’t jail every fare jumper or shoplifter in London. It simply isn’t practical. Even if you did jail them, you’d eventually have to let them go, whereafter they very well might reoffend, as they would be more desperate than before their incarceration.