3x spy doesn't behave like a 67% margin loan. Every night it gets deleveraged to 3x multiplier, which means it locks in 3x losses day by day when the market is going down.
As a result, leveraged funds are a great way to lose a lot of money even when the market is trading sideways.
Performance numbers suggest that's not the entire picture.
https://www.morningstar.com/etfs/arcx/spy/performance
https://www.morningstar.com/etfs/arcx/upro/performance
If 3x leveraged UPRO never goes above 3x leverage, it should never beat SPY by more than 3x. But it did just that in 2017 (31% vs 102%) and 2019 (22% vs 71%). Some years it loses by something other than it's 3x leverage, like 2018 (-5% vs -25%) or last year (+18% vs +10%).
Your bolded conclusion does not follow from the previous assertion.
Because 3x funds are releveraging every night you would expect that in a smoothly rising market they should produce >3x performance because each day as the market rises they are able to parley their increased gains into greater total market exposure. That's essentially what Archegos was doing: every time the share prices of the companies they were invested in went up, that created more equity which they pulled out to further expand their market exposure through even more leverage. As the Archegos story shows, this is also a recipe for disaster and ruin more more rapidly than conventional fixed quantities of margin loans.
Consider three scenarios:
A) I own 100 shares of a company trading at $10 share. ($1000 in equity)
B) I own 300 shares of a company trading at $10 share with a fixed margin loan for $2000 ($1000 in equity).
C) I own 300 shares of a company trading at $10 share with an initial margin loan of $2000 but every night I borrow 2x my equity to lever up to 3x.
If the price of the shares goes up 10% per day for five days:
Scenario A, at the end I own 100 shares at 16.105/share and have $1610.50 of equity, a 61% return.
Scenario B, at the end I own 300 shares at $16.105/share worth $4831.50 with $2,000 of margin loan and have $2,831.50 of equity, a 183% return (exactly 3x).
Scenario C, at the end I own 571.82 shares at $16.105/share worth $9209.30 with $5609.30 of margin loan and have $3560.00 of equity, a 256% return (greater than 3x).