The bigger the plane the less maneuverable it might tend to be but for example, compare the Rafale vs Su-30 MKI, Su-30 MKI is bigger and more maneuverable, in pure warload, Rafale is able to do better, but in range + warload, Su-30 is more capable, For example, for attaining 3000 kms range, Rafale would have to use its 5 central wet and heavy pylons for carrying external fuel and might be able to carry just A2A missiles but on other hand for similar range, Su-30 MKI does not need any external fuel tanks, it can do so on its own internal fuel and thus having 8 tons of load .
IAF has no clue or direction to its requirements, The requirement is not really well defined.
Firstly I do not go by the definition of light medium or heavy, just with the range, the avionics and performance,
For small countires like say Singapore or Sri lanka, smaller planes which perform the roles of interceptors are perfect. Range less than 800 kms. and ability to carry till 4-5 tons of load is sufficient for them to ensure the integrity of their air and maritime space. Since these countries are small its easy to concentrate their entire airport at one point of enemy attack without compromising other areas as its not that far to reach the most distant point.
For Big countries like Russia which have a big area, and aspirations, Smaller interceptors becoime useful to defend important cities, but then since the country is big, you need more squadrons to ensure this protection. But on other hand, big planes like Su-30 offer an excellent range and load and thus become force multipliers since these planes have excellent range, a fewer squadrons can do the job of interceptors, The need for dedicated interceptors is done away with, but that raises the cost per sortie. A single engine plane might cost abt US$ 5000 - 8000 per sortie, where are twin engine might be 10000+ per sortie,. Single engine planes are good to ensure short range roles, but the Russian doctrine is to ensure air dominance and to strike deep and ensure that the lines of communication are destroyed. And for such doctrine Su-30 makes more sense even than MiG-35. In Russian AF,. MiG-35 will end up playing the role of interceptors and tactical planes where are the tactical and strategic role will be with Su-30 due to its range + warload ability.
France is a medium country, and for them "Medium" plane was the need of hour. Single engine plane was good for them, but then they would have to maintain a separate fleet of twin engine long range strike planes to ensure the deterrent, So instead of spending money to develop and maintain two sets of planes, they compromised to design a twin engine plane that can handle different roles. But even when Rafale is being produced France is more comfortable using its Mirage fleet, the reason is that cost per sortie is cheaper. Thus it makes more sense to use more Mirage than Rafale. And the proof is that, many of the new Rafales are mothballed and kept in storage/ Its a good logic.
Lets be honest. when you have a new capable plane being produced. And France is forced to buy it (to ensure that Dassault survives) why would you keep them mothballed? Would you not retire the older plane and use the newer ones? Logic seems to suggest that there was a change in plan, and France did F up badly some place. We are talking about this situation where the purchase was cut from 25 per year to 9 per year and yet the newer planes are mothballed !!! There is no task a "heavy" plane and Su-30 MKI cannot do that "Medium" plane like Rafale can. All it needs is a good leadership to direct and a leader with vision, and certainly not followers like in IAF top brass. But consider some long ranges and there Rafale will certainly falter and Su-30 can perform without issues
You would have to argue with many NAK Browne and Raha supporters here for saying that