You're absolutely right. I'm not saying they're solvent. There just isn't any evidence that they aren't.
Both are owned by iFinex LTD, and had the same CEO till earlier this year. Total amount they have lost comes out to $1 Billion.
How are you still claiming "They may not be"?
http://article78againstnydfs.com/docs/317-cv-01882-BitfinexC...
Reversing Tether tx does nothing to recover those Bitcoins.
Edit: found this: https://www.reddit.com/r/btc/comments/7e1840/the_30000000_us...
It seems like people did in fact notice the $30m being deposited on Bitfinex and being used to buy Bitcoin, all before it was known to be stolen. Difficult to confirm a thing like this, but I wouldn't bet against it.