I don't think India's problem is imperative population & economic growth to sustain any national aircraft project, but a copious amount of delay due to external & internal factors including the budget allocation issue as Indian military needs a lot of modernisation right now to properly protect herself.
However, I believe the most damning issue is, like TF-X, schism & disagreement between Indian Airforce and DRDO & HAL. For instance, Girish S Deodhare, Programme Director of Aeronautical Development Agency (ADA) claimed back in 2021 that AMCA would roll out in 2024 and conduct a maiden flight in 2025 even though IAF (Indian Airforce) reportedly said that the schedule is very 'tight'.
Fast foward to 2024, yes CDR of AMCA is completed in 2023, but only recently in March, 2024 AMCA was approved to proceed to the prototpye stage. Now it is generally expected AMCA to make a maiden flight in 2027~2028. Who knows AMCA would suffer more delay.
At least, TF-X is on schedule that was presented by Turkish Airforce back in 2021...so far.
Well the economy pays every bill. Things at the apex endeavours especially so (these involve the best and most expensive capital and human resource after all).
India was a desperately poor country during the cold war. As a nationstate it also was coming out of long era of colonial domination, painful partition, significant wars with the other partitioned entity (including its defeat and disestablishment in its eastern wing)..... and a situation quite unfriendly to it in many ways worldwide with where there was more developed capital and human resource. These all have had massive opportunity costs that have impacted to this day.
It had no collective security arrangements with such developed countries (many of them involved in the colonial mercantile enterprise that costed India immensely) and this caused a more inward looking economic model and neutral approach to the two superpowers (which meant restricted economic access and trade).
In this environment (no export market access to capital+HR rich regions of the world, no mutual or collective defence treaties with such countries)..... scarce capital and human resource were put security wise to the nuclear program, missiles and space strategically. To some degree the navy as well and whatever could be spared to ground and air development.
Now if India had a hypothetical where it had a guaranteed nuclear umbrella from another along with strong collective defence arrangements and the related market access for encouraging an export model to flourish (to literally grow the buffers to then arrange and optimise larger swathes of HR and capital, and benefit from first mover advantage wherever possible relative to other developing parts of the world)..... simply put it would never had massive delays with the Tejas to begin with (due to the nuclear tests done in 1998, given the limited nature of the 1974 tests and the time it took given nothing on hand like the Mao-Stalin agreement in China's case in exchange for providing the scale of PVA in North Korea that Stalin demanded from Mao).
Without that Tejas delay, there wouldn't be a cascade of other delays in this ecosystem and now all the way to AMCA.
i.e the AMCA would have been done and flying with a "cold war western inherited economy + strategic ecosystem inertia etc" but along with no nukes (and delivery, required sensoring and next set of steps and elements for higher tiers) and the reduced strategic independence (especially for a country this size and the fissures it could have created given the colonial experience....and if thats worth a tradeoff for the extra GDP).
Say numbers A, B and C per capita (say something equivalent or better to what we have today on these) during the 1990s when the Tejas was taking shape....and also had to compete with the nuclear weaponisation and triad (SSBN) completion and the way the powerful+richer countries then perceived and took their own measures on all of this.
But it is what it is, we needed the nukes, missiles, space and ability to manage statecraft (internally and in our immediate neighbourhood) independent of "easy/forced side picking" in the cold war as far as possible.
This in hindsight has been detrimental to our economy in the longer run till the cold war ended and course corrections were finally done and are ongoing.
So its very connected to the economy, there is long legacy from the cold war in many apex insitutions and working processes....and even basic capital and HR still.
Thats the whole point of an economy in the end, it has to grow so you have the margins to take a kittyhawk wright brothers craft all the way to an F-22 and beyond.....by the vast growth, arrangement and praxis of the capital and human resource and processes involved over the periods of time needed for this to entrench and become second nature in their respective manifolds.
But you live, you learn and you improve and catch up where you are behind, and at same time understand certain things you did were also correct routes in a very non-ideal world at the time.
Its good we got some very high power stuff things right and guaranteed....while being outside market and collective security access so long and the tradeoff is a delayed 5th gen AF platform today....that's fine. As long as the deficiencies are being learned from (both regarding the economic levers to gain and grow more and more capital and HR and also how they are to exist and function at every apex endeavour known to man)....which in India's case is a long debate, but there is notable progress.
But with a country like Turkiye or South Korea, its very different. You have different intensities and contexts here....and the immediate 1990s post cold war snapshot can be looked at for it for relative inflections and inheritances for today.
i.e There are simply things you didn't have to worry about or impacted you way different compared to India's situation....that create different routes in critical decision making. This doesn't take away from India's own peculiar mistakes within the world setting it had....but in end its not surprising we have nukes+missiles+space but a slower 5th gen platform maturity.
Turkiye is very unique in how it sits near Europe (and then Russia, Middle East and Africa too with no open ocean like in India's case), its evolving relationship with NATO partners and how it harnesses what it has needs wise for its 5th gen. It perceives it absolutely has to as it has adjudged certain things in its security environment in what it has and doesnt have at hand. This intensity changes when you say move to Indian context and backdrop.....the whole geography changes and there is simply no NATO or same cold war experience (w.r.t economics and so on). So we say have the nukes, but we need to improve on lot of things Turkiye has in better working order already.