#1 You would have to coinjoin every single transaction which no one does (especially after recent events). That would get expensive fast in time and money. #2 Is a stretch. Payjoins are obfuscation. They don't hide/encrypt amounts. #3 Is weaker on a transparent chain. Counterparties can easily figure out which address they sent to and watch where it goes going forward. Even third parties can most likely figure it out given any two combinations of amount, time, and sender address.

Last part reminds me of this meme