From what Ive seen so far, I can agree with this. From every professional trader I've heard speak, they all how some quantifiable edge that they can look at.Live testing (small size) gives you a picture of where (or if) your orders might get filled. In many cases, a backtesting model can't be trusted without this live data, so live and backtesting should be combined. Once you're able to build a single strategy with that information, you can then build a strategy farm. That's a whole different ballgame. You have to be some form of a quant.
I recently saw an interview with a trader at DRW and all he talked about was expected value and finding your edge. No moving average crosses, no fib retracements, no candlestick patterns. Just hard statistics about where is this instrument trading now, and what is our expected value around it. This was really eye-opening to me.
For me personally, I would have a really hard time trading a system or method that I didn't personally crunch some numbers on to see where the edge is and what it looks like.