Quite why the platform team allow people to stand right in front of opening doors of busy trains meaning it takes ages to unload is beyond me.
It has been an open secret, for a very long time, that there has been basically no management attention on what is happening on platforms to support the timetable beyond an attempt to save money in the employment of staff. On the latter point I would cite the shortage of staff numbers, the fact that some are employed on inferior terms and conditions to their colleagues by contractors Carlisle, and the removal of most platform staff from other nearby stations, e.g. Manchester Airport.
The employment of a large number of agency staff who are provided with very little or no railway industry training and familiarisation to shout at customers has made the problem which you describe worse, as has the painting of a red line on the platform (which was far too far back and had to be repainted much closer to the edge), because psychologically it makes customers feel more anxious of missing the train as they wait. This makes them more anxious to board the train as soon as it arrives, and the red lines, announcements, and agency staff have no effect on this. Additionally, the large number of long-distance trains which serve these platforms brings large quantities of luggage, which takes time to unload and load even if the problem you describe doesn't occur. The inappropriate rolling stock with very narrow doorways and very limited standing space, especially the class 158, which is commonly found calling at these platforms, is also crucial in station overtime. The agency staff have also been known to inhibit the dispatch procedure by standing in the way, or stretching or making other motions interpreted as emergency signals by other members of staff (unsurprisingly for staff authorised to work on platforms having been given no form of dispatch training).
In other words, from my experience of several conversations directly with the staff who work on these platforms, and from what I see when I travel from them myself several times weekly, there is very little or nothing one person can do to stop the current crush around the doors. The consequences on timetables on 3 minute headway where both trains are long-distance services and which have narrow doors at the ends of carriages are and were totally and utterly predictable.
The recent amendments to working to try to ensure that both circuits are not occupied simultaneously on these platforms where trains are short enough (which is almost all of them) seems to have helped. I would question why it was ever as it was in the first place, though. The screens in the lounge upstairs were initially programmed very poorly and displayed very confusing information, which limited their effectiveness at trying to get people to wait upstairs. They're now slightly improved, as is information at platform level.
There is no substitute for a properly supported and well remunerated and motivated workforce, of appropriate strength in numbers, to work on these platforms. It is my belief that performance under the current timetable cannot be easily improved without it. Plainly though, train companies don't want to pay for it.