Here's a different view of the Portfolio Visualizer comparison - 10 years only.

Portfolio Visualizer being limited to 10 years is a big problem but is good as a "sanity" cross reference.
Did you look at the testfolio link I posted? When I first learned of testfolio I did several cross-checks with PV and found they agreed, so I feel confident in it.

Also, as I mentioned, the annual rebalance backtest gives an artificially high CAGR because of the fortuitous interaction with the 2022 mini-crash. To get a more realistic number you need to look at semiannual or quarterly.

Or, make 12 annual rebalance runs beginning with each month, then take the average. When you plot the value curves on one chart, there is a startling divergence around 2022, looks like an open shark's mouth, some went up and some went down. Other than that, all 12 curves track tightly.
(I did all this with Excel 2003.)

The historical reference information is... difficult... to get at these days.

Yes. But with a bit of cleverness you _can_ get it. Of course, what you need is the "adjusted close" prices, which includes dividends.

-------------

The BIG problems is the inception dates of BTAL(9/2011) and TQQQ (2/2010). That period doesn't include things like the bear markets of 2001 & 2008.

I have a feeling that TQQQ would get absolutely crushed in a bear.
The 2022 downturn, S&P500 lost -20%, TQQQ lost -80%, QQQ lost -34%.
Jan 2001 to Oct 2002, SPY lost -31% and QQQ lost -53%.

And the issue right now is that everybody thinks a bear market is overdue. ;-(

I played around a little bit trying to find a timing method for TQQQ and didn't find one that worked good enough.