Well that's why each users on the exchange will have a unique deposit address....
Not really, because:
- people don't regenerate the address before each deposit
- people will have the address copy-pasted in their wallet address book and reuse it even if the exchange regenerates it each time
- doesn't solve a deposit followed by multiple withdrawals in smaller amounts
For the address to be significant, it needs to be handled under the hood by the exchange, as a dust/signature.