Arf, sorry for my confusion. Thanks a lot. I've corrected my post and my answers accordingly, i think it's good now. I indeed meant address every time i wrote public key. But with that correction in mind, my interrogation still works. Not sure what you mean by privacy score and if it applies to ethereum in general or a particular exchange. I just wanted to know if my scenario mentioned above was possible (finding the sender's wallet by data mining the exchange's wallet transaction around the time a transaction has been made, even if it takes several attempt to narrow it down one repeating address that keeps on appearing during a transaction with that specific receiver).
Cause i'm not sure that when you say "Exchange wallets or addresses are very easily to be recognized." it means that it's indeed possible to trace back to a sender or is not related to my issue.