And after such a long reply, maybe these additional short answers would make more sense.
A single indicator with standard settings is considered a good and not curve fitting indicator.
Obviously, you're reserving the right to choose which indicator exactly to use? So, that's you're degree of freedom. And yes, you've just increased the possibility to overfit, because you granted yourself that degree of freedom. It doesn't matter that you will use only standard parameters, because there's so many indicators to choose from.
However, When I put many indicators with all standard settings on the chart, It is considered a curve fitting system although it is profitable in back test?
Now you also have very large number of indicator combinations to choose from. And you can optimize the hell out of it, until they perfectly fit. Not bad for only standard settings.
Is curve fitting is not only about parameters?
Obviously not.
