I've called the 24hr toll free ANA number in the past but I choose the Japanese option and I've gotten through in 30min or less each time. Looking back at my phone records, the two calls were 25m and 37m in length so subtracting the 10-15min conversation, the holds would have been about 25min at most.
OP's assumption may have some merit if the English speaking reps are also on the Japanese line and anyone calling into the English option would have to wait until the next English rep is available.. at worst they may be placed into the back of the queue to roll through again if an EN rep isn't available, but I can't speak for ANA's internal workings.