I have written my response. I think it makes sense:

If you can understand my frustration, then I presume you have an answer as to why, for example, the 18.36 was reduced from its usual 8 to 4 carriages this evening? Or why the same happened to the 18.18 a couple of weeks ago? Or why many of the trains between 7am and 9.30am from Honor Oak Park are consistently dropped in carriage size, making everyone's journeys unbearable?
This system is an absolute sham.
It's easy for you to say it's difficult for all travellers to find a seat at some point, but it doesn't have to be this way does it? If one day you have an 18.36 with 8 carriages, then it should be like that every day, shouldn't it? That's simple to understand, but it doesn't seem to mean anything to Southern. Maybe you're experimenting with your radical 'weighting system'? Well don't experiment on us. Just make all peak carriages at least 8 carriages and we might just start getting somewhere.
As for cancellations with no human apologies, 'track adherence' issues (leaves on the line - can no-one rid us of these unexpected leaf-falls?) and defective rolling stock (the driver's having a sandwich), I, and the rest of your 'clients', have had enough.
We ARE sardines, and we are caught in Southern's uncomfortable, overcrowded nets.
A question to your bosses: What is going to be done about it?
Jon Lloyd