Thats an additional fact that the amount is in line with the amounts that would be deposited into any big exchange.
If Coinbase minted USDC whenever someone deposited, you would see the same kind of growth.
The basis of your entire post is assuming impropriety based on pretty normal behavior with the addition of the business quirk of when USDT is created.
The ability for impropriety is a good enough reason to avoid it, and their unilateral willingness to do so without any discussion can reinforce that. But people thought everything you thought since the beginning of Tether in like 2014 or so, but the reality is that it “only went fractional reserve” in 2018. Its kind of like they threw up their hands and said “well people think its a ponzi anyway might as well cover this business debt!” The irony being that the NY AG investigation actually proved that prior to 2018 it functioned exactly as promised, barring their 2017 distress by having nowhere to put their fiat deposits.
But if you assume that it hasnt come crashing down because Bitfinex does what they said, then it still does make sense: crypto prices pump after Tether mints because it is people depositing into the exchange and then buying crypto.
Any way glad USDC and DAI are growing a lot now, which have grown by the same orders of magnitude.