After reading your initial post as well as your subsequent ones, I do agree with the majority of what you have said. For manual traders, I have always advocated to skip trading on a demo account and start with a live account right from the start (with a small amount, of course). Even a small live account will allow a trader to feel the emotions, and start working on following his or her trading plan and discipline. At the same time, manually (by hand) backtesting a trading strategy is very prone to personal bias and look-ahead bias.
With that said, I think you could have phrased your opinion a bit more clearly. You seem to have used the terms “discretionary trading” and “technical strategies” interchangeably; they are more opposites if anything. A “purely technical strategy” as you stated, usually refers to a strategy that is 100% mechanical, as in algorithmic. By that logic, it wouldn’t make any sense to backtest such a strategy by hand, rather an automated backtester would be a better solution. On the other hand, a discretionary trading strategy may use technical analysis, but would also require the subjective opinions of the trader.
Every point you have addressed applies only to discretionary trading and not so much algorithmic/technical/mechanical trading. I think this should be made clear so that new traders reading this thread do not get confused or form bad habits.