Its not your fault. Many Indians are too blinded by nationalist pride to see the obvious.
The last proper standard rifle IA had after the SMLE was the 7.62x51mm FN-FAL. It was a good and accurate rifle and was much favored by NATO in the early 70s. But then the world had moved on to the 5.56x45 mm round which was lighter hence more stable, more rounds could be fired and was able to be fired at full auto, something impossible for the .30 caliber.
Further to this DRDO was sent a proposal for a new rifle in the 80s and the DRDO set to work at their own leisurely pace. Meanwhile in Sri Lanka the army learnt a bitter lesson that the FN-FAL had passed its usefulness and the IA needs a new lighter weapon. The FN-FAL was proving disastrous in guerrilla and counter-insurgency operations in Jaffna but the DRDO rifle was yet to be introduced. The IA purchased many Romanian kalashnikovs as an ad-hoc measure.
Around 94-95 the INSAS finally made its debut but to the dismay of the IA it was not what they had expected. The rifle was shorter in length but weighed almost the same as the FN-FAL, had 20 rounds ammo just like the FN-FAL and provided no advantage of using the 5.56 mm round which was the main reason why the army wanted to field 5.56 mm rifles. The IA was handed a 5.56 version of the 7.62mm FN-FAL rifle. It could not fire full auto like other 5.56 mm rifles, it did not carry a standard 30 round mag like 5.56 mm rifles worldwide and it weighed as much as a 7.62x51mm rifle minus the punching power.
If you visit the archives and read then you will find the IA criticised the INSAS during Kargil conflict.
Arjun is the most advanced MBT today? From what analysis have you come to this conclusion, please elaborate on this. How does the Arjun fare against the mighty Leo 2, Abram, Challenger 2, LeClerc and Merkava tanks which are universally considered the best in the world of MBT?
What, I repeat, WHAT advantage does the Arjun provide over the T-90 that IA should pay more for a tank that is too heavy and difficult to mobilise? How is the army supposed to deploy a 58 ton tank when infrastructure of rail, bridges etc. have trouble supporting anything over 50 tons? What is the power-to-weight ratio of the Arjun? How many T-90s can be purchased for the price of one Arjun?
The T-90 is already delivering whatever the needs of IA are. And India is fielding 1500 T-90s as of now. So instead of replacing all 1500 T-90s with 1500 Arjuns it would make more sense to add another 1500 T-90s to the mix. Why waste so much time and money on a tank that is the same as the one currently fielded by the IA?
Commanche was a high-tech stealth helicopter built by USA but it was scrapped later because the US army found it obsolete. Now you might wonder why was a stealth chopper considered obsolete, after all stealth age has just started right? Because the missions required for the Commanche was already fulfiled by cheaper, simpler, easy-to-use drones.
In the same way, Arjun is obsolete because whatever Arjun can do is already being done and done beautifully by the T-90.
... why dont you answer my 2 simple questions? 
