This is exactly how the output is designed to work. The Word Clock output has a 75 ohm source impedance and the 192 Word Clock input has a 75 ohm termination. The result is that the signal level is dropped in half. This is standard procedure for a high frequency signal such as video or AES/EBU. If a person needs to drive multiple destinations with such a signal then they need a distribution amp.
SYNC I/O was meant to use its Loop Sync output to clock the I/O boxes which would leave the Word Clock output available to drive another load. The current release of Pro Tools doesn't support this function. There is also a Word Clock output on each I/O box for driving additional loads.