That depends on how the tumbler is implemented. If the transaction from sender to receiver is instant and from a single address to another single address, well then yeah it's obvious. But if you batch the transactions of thousands of users over the course of a day for example, and make sure to split the amount to send to multiple addresses with random values, now the only thing that you can correlate is that one of the thousands of senders might also be one of the seemingly tens of thousands of receivers. If the tumbler is allowed to spread it out over multiple days or weeks or even months, well then good luck ever correlating the sender and receiver.