Not read any P&O reviews but I guess they might be suffering from the traditional diners not adapting yet. The other thing is people will tend to try to fit around the shows so you get peak times then.
One of the tricks with the freedom/anytime/freestyle dining is to find out when the queues start and get there 5 mins before adapting to the pattern that forms on your trip. Ask when they expect the waits to start and aim to eat just before then and see how it goes.
Most people just don't work this out and if they want to eat at 8:00 get there at 8:00 and then end up eating at 8:30 and getting upset about a wait, then do the same thing the next day.
If you still want to eat at a peak time just plan to get there a little early and have a pre-dinner cocktail while you wait, if called early take the cocktail to the table.
want to eat at 8:00 and there is no queue at 7:30 go then, sit and take your time ordering and eating the starters so you still eat at 8:00 ish anyway.
Another trick is you don't have to have all the meal at the same time, if an early meal is going to be too much skip desert and take that later you can always return to the dinning room for desert and coffee after a show for example, or just hit the buffet.
Another thing to watch is the port schedules this can skew the timings for a day especialy a late departure.
One thing that is worth thinking about is moving your normal schedule forward or back to avoid the peak times, early B,fast,early lunch, early dinner, late b,fast skip lunch early dinner etc. the one down side to an early dinner is the long evening, fine if there are a couple of good events on, one thing that traditional late sitting does well is split an evening.
I would not worry too much about the food side of things it's not like we go hungry on a cruise, go with the flow and try to make the most of the other things going on, try the buffet or alternative dining options.
We still like the traditional cruise experience(no thinking required) but the flexable approach is great if you adapt to it and make it work for you.