It is actually true that many prefer the better posture that seats designed for it have. It is also true that the appearance of seats with deeper padding gives an illusion of comfort, which may or may not exist in reality. Given the different needs of the very intensive services we now have, the imperatives of weight-saving, easy cleaning, good passenger posture and of course with a railway run for profit, - low cost of ownership are paramount.
Thank goodness the railway companies are not responsible for car seats, office furniture or fitting out my lounge.
You state "It is also true that the appearance of seats with deeper padding gives an illusion of comfort, which may or may not exist in reality." I will agree with that; the comfort 'may or may not exist in reality'. However, may I assure you that, by comparison with the latest offerings on the Central Division, the final generation of slam-door main-line stock (with the exception of the refurbished CEP compartments and their poor arm-rests) really was much more comfortable - it is not a figment of my imagination!
I do not require a railway franchise operator to provide me with uncomfortable seating in the interests of my posture - I am altogether too old for a nanny! In any case my 600 miles per week, over 27 years, of sitting in CIGs and BEPs and VEPs has done my posture no harm, whilst fifteen minutes on the modern seats under discussion brings pains to my nether regions!
I don't doubt that there are reasons why these appalling seats have been chosen, but don't try to tell me that I am imagining the more comfortable past.
The world is a big enough place to accommodate some who actually prefer the new seating. That I accept, and you may be one of them, but I think them to be a small minority - I've yet to meet one in person.
Could I end with a proposition? Why don't you write to the Palace and suggest that the Royal Saloon is refurbished with these wonderful, new, comfortable seats?