I am using my system with success.I do use discretion as everyone should like high impact news,major bank rates change etc.
With any system discretion should be used.Because we are dealing with human emotions greet/fear which reflect on price high discretion is a must over systematic systems so edge is traders knowledge which is subjective to measure.
I tend to agree with you that even pure systematic system requires human discretion.To me system is a base where trade has high probability to succeed but even then you must be looking at time of day ,news impact to pull the trigger.
regards
In trading, you have to be defensive and aggressive at the same time