But probably QuantConnect provides the data which you can't get from an independent app. I might be mistaken.
That begs the question for OP: how does the prop firm want to test it? What exactly do they ask from you?
Stock indexes can also lose 40-50% within 12 months but they are considered of better value than cash in the long run. And GBP lost to dollar almost 50% within 12 years. Would you say that dollar was better for storing value than GBP 12 years ago? As far as I can tell the less the asset depends...
What is a value of something that is printed and controlled by the govt and subject to its mutable policies? Today it might have value and lose it tomorrow. Isn't Gold better for storing value than printed money? What would grandparents say to that?