If the market did the same in duration for 10 years, it does not mean that it will perform the same in the future but it may.
Do you think backtesting is reliable?
Of course, it is reliable. I think that nowadays the basic principles of how does the exchange market work haven’t changed. Especially psychological factor of how people think when they are trading. We all are still making the same mistakes. So, I think, you can rely on your backtesting results.
And very important difference between demo account and backtesting is that you can test a looot of strategies with backtesting, when in demo account you could test at least one.