IMO they need to accept that they are not a big enough operation, especially currently, to process that many flights.
Let's see what effect these additional 400 staff have in April then. But it was never a pleasant experience even pre covid, and a large part of that was because they squeeze in extra flights and passengers at every opportunity, instead of accepting that they are an airport with only two runways and two and a half terminals of questionable efficiency.
I've seen over and over a ramp up in demand causing huge issues in various industries in the post covid recovery period, and it's obviously travel's turn now, so I understand that and it's a valid issue for them.
But above all, if passenger safety is now at risk then action has to be taken now and decisions taken out of current management's hands. Nobody's wants to hear that a child was crushed in a melee to get to a plane on time, just because hiring extra staff was not in their lean budget or they couldn't make decisions in time. It may seem dramatic, but that scenario seems more feasible to me each day at Manchester Airport.