EMA Cross?
With one of the biggest fears / downside to starting investing in TQQQ today being - what if this is a bubble and we're at the top.
What is wrong with just doing a long term ema cross strategy like 100/200 ema cross on daily chart? Back test on QQQ shows max DD is like 13%. You completely avoid two of the biggest crashes in history - dot com crash and financial crisis.
The risk profile just depends on the investor. Theoretically you would have around 40% dd on TQQ or 26% on QLD. So it would be up to you to decide if you want 100% of your account per cross or 50% or whatever allocation you want to account for risk tolerance.
Downsides I can think of are just frequency of signals - currently very overextended so might take a while for next entry and if you have a losing trade the money is just gone unlike buy and hold.