Absolutely not. The easiest thing in the world is to backtest until one finds a winner. Just use Will Rogers' rule: "If it don't go up, don't buy it."
That's not backtesting, at least not proper backtesting. Properly-done backtesting has significant predictive power. Will Rogers' rule doesn't.
In
response #13 I presented a 37-year backtest. I didn't build it by trying 100 things until I found one that works -- I just looked at the historical performance of a well-known strategy. You can find 60/40 backtests everywhere, but I added some value by generating synthetic 3x data to approximate the HFEA performance over a longer timeframe. That gives you a longer sample period to get a feel for how the strategy behaved in past market conditions.
At the time I hadn't heard of HFEA, but based on that test and others, I put a significant chunk of $$ into UPRO and TMF -- and UGL (2x GLD), in a 40/40/20 proportion. Unfortunately, as per my usual, I pulled the trigger at almost the worst possible moment in the last century, or at least since 1937. I opened the position in August 2022, and as a result it instantly went into drawdown. Trusting in the historical performance, I gritted my teeth and hung on. Based on my testing I chose to do annual rebalancing, though in 2023 I called an audible and skipped the rebalance. I could see TMF had more "down" in it, so I chose not to rebalance to a larger TMF position. That turned out to be a good call, as TMF is down 30% and UPRO is up 20% since then. (Exiting TMF entirely would have been a better call, but oh well...)
Result: in October '22, 2 months after opening the position, it was down nearly 40%. Thank God I didn't open it at the start of '22, or it would have dropped 65%! Then it went mostly sideways until last November. Last month it finally clawed its way back into profit! With the recent drop it's down about 3%.
The 37-year backtest may not be as good a prediction as it used to be, because things have changed -- no more declining interest rates, etc. But I think a backtest like that is the best prediction we have. It's not a data-mined curve-fit any more than standard 60/40 is. It's just a test to see how an HFEA-like portfolio would have performed in the last 40 years.