Hello Dommech,
your method is just fine I think, very similar to what I do. Also, you are right that there is no guarantee, and I think I make this clear in all of my courses. We never know if a profitable EA will continue trade well. It is just the same as to know where EURUSD will go tomorrow.
But the thing is we wan to put more things on our side before trading, anyway we would be gambling, and you will never see me in the casino :) No way!