So far, I'm not seeing that. Gotta specific date, chart, link, we could all look at? EDIT: Nevermind, I see what you're saying now.
I did a quick analysis of TQQQ vs QQQ for the past 5 years. TQQQ's correlation is rock steady at 1.0 and Beta is pretty stable at 3.0. The Beta does fluctuate slightly during market dislocations such as the covid crash but even then it was extremely close to 3.0
But if I cherry-pick the amount of TQQQ data I use, and the chart display settings; I get to make it look like the sky was falling (Daily % Chart):
If I were going to put something away for 30 years and not look at it I wouldn't be afraid of TQQQ. If you believe that the US economy will keep percolating along and that technology will continue to evolve then the Nasdaq 100 (QQQ) will probably continue to increase in value over time as new companies are added and the poor performers are chucked out. A 3 times derivative should perform somewhere around 3 times as well. The trick is not to watch it.
. On the other hand, SQQQ is down 99.25% the last 5 years so you'd have to make 13,333% return moving forward to break even.
I appreciate all the interesting perspectives offered here, and I see that there are considerations I've yet to take into account. I'm going to digest the comments made and do a little more research before I comment further. Thanks to all who've contributed, in particular @wmwmw, @userque, @Nine_Ender and @R1234.