Solvent usually means being able to pay ALL of your obligation in the LONG term so your claim that they are solvent because they manage to cover SOME obligations in the SHORT term doesn't mean anything.
Where can I find the info on billions that they exchange yearly?
Shows a decline in market cap from $83B in May 2022 to $66B in July 2022. That represents $17B in redemptions over a few months. That represents Tether net paying USD to USDt holders.
That they keep paying out billions each year in dollars to those who request it?