How will indigenous equipments run into supply problems? The supply problems are a result of imported supply chain, not Indian made parts.
As for making large scale production, regardless of complexity, the parts are made by machines to a good extent which speedens up the manufacturing by the same scale as it has become complex. Do you know that India makes 60 lakh big vehicles like cars, trucks, tractors, buses etc every year and over 2 crore 2 wheelers a year? This is despite all of these increasing in complexity compared to even 20 years back. Do you even understand the scale of automobile production that India does today? Why is it so hard to understand that similar scale is possible in defence too?
As for P51 mustangs, USA produced nearly 5000/year of it. USA used to produce 40k-50k planes every year during WW2. This is over 100 planes per day! And you behave like you are shocked by a number not even 1% of that scale if proposed to be done today! Defence production is less than 0.1% of the peak capacity shown during WW2 because of political reasons to prevent arms race and oil/resource trade route disruption, not because of inability
Do you think indigenous equipment doesn't have supply chains? Do you think Indian component and subsystem suppliers have infinite capacity? Do you think our indigenous jets use only indigenous components? Like it or not, there are bottlenecks everywhere.
For instance, HAL has hundreds of suppliers for the Tejas Mk 1. If they want to go from, say, 16 aircraft a year to 24, that means ensuring every single one of those suppliers can keep up with the increased requirement of parts, or you have alternatives on hand. You can't just double capacity by saying you'll double capacity.
Sure, localised supply chains are often easier to manage than supply chains that ate spread out, but you would very quickly hit an upper limit in India as well. Moreover, do remember that the Tejas Mk 1/1A, Tejas Mk 2, and AMCA will have a lot of common subsystems, which means those suppliers are also potential bottlenecks.
Now, coming to mass production, you are ignoring the simple fact that while you can build 60 lakh vehicles a year, you are able to do that because there is a commensurate demand for 60 lakh vehicles. If the market demand was 10 lakh vehicles, would you still manufacture 60 lakh?
Moreover, even a car is nowhere near as complex as a submarine is, simply by looking at the number and type of subsystems involved.
Even if you could somehow manufacture 100 submarines a year (which is completely absurd to start with, but anyways), do you have any idea of the number of submarines you would need to order to do so? China and America today make 60+ submarines of a single class, and they generally have a production rate of 2-3 boats a year.
Again, production depends on bottlenecks and the supply-demand dynamic. If you gave HAL a order for 1,000 Tejas Mk 1A aircraft today, they'd start cranking out 60-70 aircraft a year in 5-6 years. There is a practical limit on production rates, no matter what absurd rates you can get from theory.
Oh, and if you want to compare, a P-51 in today's money would be around 6,00,000 USD. In contrast, a F-16 costs around 50.75 million USD today. Think on why that is the case, would you? And be more practical, please.
