GTD shouldn't even be under consideration unless you're doing 20k+ miles p/a.
That's nuts. Even if you only do 10k miles PA, better residuals, cheaper list price and cheaper running costs make you a saving from day 1 and every month you have it - the question is, will the person deciding think that the GTI is worth the extra money? You'd have real bother doing 5k miles PA with a DPF, but 10k miles is fine.
I have set myself a limit for running a car (to allow me to do other things), and if I was PCPing and copping for all that interest rather than having bought outright and just putting back the depreciation into savings towards the next one, I wouldn't be in an R right now.
FFS Mh, does everything have to come down to counting a few pennies. In my opinion, a Diesel is a compromise. A compromise only worth making if you do big mileage.
A diesel car is plainly not suited to short journeys / city commutes / low mileage. I just cannot understand why a GTD would even be considered or why mpg would be such a huge fixation for anyone who does low miles. If you do low miles, as I do, rejoice! Get a petrol car, ease off on the mpg fixation and enjoy the car. Life is too short.
What is a compromise? is a GTI a compromise over an R (which costs more to run), is an R a compromise to an Audi RS3? You could go on and on on that argument. Everyone has a budget in mind when they run a car.
You are entitled to your opinion, but it purely that, opinion. It is a FACT that the GTD costs less to own and run on far less than 20k miles PA, and £50/80/100 a month difference is not pennies.
Some people would concern themselves more with what they're paying at the pumps every week than what comes out of their account for the car itself (I do think Chris is one of those people!

).
For me the R is worth the extra running costs, for others it won't be.
I find it mad that people will increase their depreciation by £100 a month for a few extra gadgets on a car that is already rammed with standard equipment, as options end up hugely expensive considering how little value they hold - but for others they want that DCC/Pro Nav/sunroof etc.