This scheme would likely have fallen apart when they were printing and BTC continued to go down...they were no longer able to keep the price rising, so they likely weren't able to buy more USD than the USDT they printed.
To me, it really looks like Tether was propping up a significant portion of the valuation of BTC for a few months; they were printing enough to buy roughly half of all miner output (and in a market where most coins are in a state of HODL, the miner output and demand for it determines the market price). Probably much of the climb up to 10k was market manipulation by Tether. Yes, lots of dumb money went into the market in response to the climb, but when the printing slowed, the market fell pretty fast.
So, I agree it was ballsy, but I strongly doubt it's fully backed even now. I think when they started printing a hundred million Tethers every few days is when the market began to tip against them, and they were desperately trying to keep the BTC price climbing. They're gonna walk away from this scam multimillionaires, unless they go to jail, but they've never been sitting on 2+ billion USD in cash reserves (I just checked, there are currently 2.5 billion Tethers in circulation). I find that idea literally unbelievable.
Frankly, I'm out of crypto until Tether is, or until there's an audit by a reputable firm which I'd wager will never happen. Somebody's gonna get hosed on the deal, and it's gonna be pretty much everyone involved in crypto who isn't running a massive ponzi scheme, I'd guess. If there's anyone left that meets that description.