Isn't India like a really big country? And what we consider 'curry' can be as far removed as Afghanistan (or even Persia as you point out with the origin of naan) to bhurma, nepal to sri lanka.
It's like saying only Naples style pizza is the only real pizza - there are many very similar dishes all over the Mediterranean from spain to turkey and you can't start knocking a new york or chicago style pizza just because it's not a Neapolitan.
Lots of food styles can be done badly or very well - even a traditional english sunday roast (you know in the middle ages the french court sent chefs to England to learn techniques for roasting joints).
I think curry in England must bear some relation to our history of roasting meat - concentrate on the gravy!
I think Indian curries are unique to the spices used and found in India as well as the ingredients.
The real ones.
In fact traditionally curries aren't even consumed in large amounts in India instead sabji's are. Curries are cooked less frequently or on special occasions.
Like the list I made above. There's only one curry there iirc
Like I said before most won't even know what real Indian food is.
I've travelled all over India and yes it is big and the cuisine is different but the majority of Indian restaurants are based on Punjabi cooking from the north.
You do get south Indian places that do stuff like dosas. They have completely different breads to what Punjabis use too. They are watery and very thin.
Also the rest don't really eat chapattis like Hindus the majority eat mainly rice.
But your comparing very small differences in like people in Scotland eat haggis, black pudding, etc. But British cuisine as a whole can be defined.
Steak pies
Sausages and mash
Fish and chips
Gammon steak and chips
Beef stew
The list goes on as you know
There will then also be more localised dishes ate more in certain areas or unique to them.
Like South Indians eat a lot of seafood.