If you have equal numbers of captains and FOs, the lines will be built equally since each flight requires 1 of each. My guess is an equal amount of open time is available to FO/CA. Captains throwing shade on FO's picking up open time is hypocritical since they, as a group, are picking up just the same.

Now if CAs were getting junior manned, extended, etc. and FOs were just gobbling up OT, I could see the argument. However, I haven't seen those occurrences mentioned in any of the threads.