"Chicken Jalfrezi, mate, and add some extra chillies! I like it 'ot!! And give us some onion bhajees and a ration of Bombay potatoes!"
The cook in the kitchen pulls some leftover chicken from the fridge, ladles two slops of garlic/ginger gravy into a frying pan, adds two slops of "medium-hot" sauce in as well, and chucks in a few slices of red or green peppers. Adds the chicken, heats it through, sprinkles it with coriander leaf and there you are. the Bombay potatoes get two slops of the "medium-hot" and are warmed through too. That's it, basically.
I grew up on "Curry House" food. Far more exciting than roast lunches or egg & chips, ham & chips, omelette & chips, or Shepherd's Pie. I don't know what I'd have done without it, to be honest.
When I moved to Venezuela in 1981, there were NO CURRY HOUSES!

OMG!! What was I going to eat?
That's when I really started cooking Indian food. Bought a few authentic Indian recipe books and worked it out from there. On a trip to London in 2001, I went to a place called "Chutney Mary" in Chelsea, which boasted "authentic Indian cuisine", and had 5 chefs from 5 different regions in India to prove it. A million times better than Curry Inn, totally different flavours, each dish a gem. Then, a few years later, I went to Moti Mahal in Soho - run by the former chef to the Indian PM. Tandoori style and, again, unbelievably good. This time I went to Dishoom and to Masala Zone. There was a "hot" dish from Andra Pradesh, with paneer and a tomatoey sauce. Incredible (and incredibly hot) but totally different from a Prawn Phaal.
The article is dead right. The idea you can have a) chicken b) prawns c) lamb d) vegetables in a a) mild b) medium c)hot sauce, AND have it served from different regions by adding another ready made gravy is no longer valid. It was great 40 years ago, but now the authentic stuff is here. Balti? I think that's a Pakistani/Birmingham dish.