For this question, you have to imagine what would occur if you requested such a weather deviation from a controller over standard VHF radio. They cannot respond with "ROGER" or "WILCO" as they would not work for this request, and "AFFIRM" would not be a suitable response in order to approve this change in routing/clearance. To issue a change like this, ATC would have to read out the deviation routing to the aircraft, who would then read it back. This would work the same for CPDLC communications, so "AFFIRM" cannot be correct.
This leaves only "STANDBY" which is certainly an acceptable response to such a request, whether over VHF or CPDLC.
Your Notes (not visible to others)