You're confused on the meaning of discretionary. If a strategy can be coded, it is not discretionary. If it is discretionary, that means it can't be coded. At least until AI is invented.
There was a thread once about an ATS that made steady money for three years then gave it all back and more in one month... lots of learning experiences with trading, one just never can be sure when they are done learning. Other than that it's a bowl of cherries...
I think the quote that reinforces your point is "life's a box of chocolates ..." I don't trade ATS but I'm curious if anyone here that does would give back three years of earnings in a month without shutting it down well before they went that far? There is no discretionary trader that could make "steady money" for three years without seeing there was a problem, that something had changed, well before he gave it all back. I don't believe successful automated guys are all that different. Reason must rule.