I can only remember from when I started eating curries in 1989 and even restaurants when from the sublime to the ridiculous in the same street ( I started eating curry in Preston, church st).
It does seem however that when I'm back in the U.K restaurants that used to be good, have gone bad... I notice more sauce, less meat, more chunks of onion, less taste in general. I can only really comment from the perspective of living in France where I talk to many restauranteurs. It's the same story, ever increasing food prices and reduced margins. Many restaurants in the fast food trade like to keep there prices fixed, so in order to keep ther margins they have to reduce quality. I know a pizza resuarant near me that hasn't increased their prices for about 10 years, the pizzas used to have things on them, not any more.
Obviously, restaurants have 2 options they either decrease quality or increase the price. Using pastes and sauces is one way of reducing costs. I have absolutely no idea if the good or bad curries I have eaten have used Pataks or any other jarred sauce but from personal experience whenever I use a premade paste I notice bitter undertones and too much salt, this goes for jars of ginger/ garlic puree.
I also notice when I come back to the U.K that a menu in any pub or restaurant has to describe the ingredients/ cooking method and various other Jamie oliverations such as 'suculent, gorgeous, fantastic.....' . In France it would be called ' Beef with potatoes'. I'm sure this is slipping into the curry trade as well. People don't wan't to eat Madras they want specials and they want to know every detail about it.
Sorry to be wittering on but I'm still on holiday so I had acouple of beers....