That's very impressive, but don't forget that Tether is like a central bank...they can "print" money whenever they want (USDT is their money). Just check "whale alerts" on Twitter, and you can realise that only in January they "minted" more than 1 billion USDT (equally with 1 billion $).

Tether is definitely not a bad business, but I think it is not the best busines in the world