The base armor of the T90 is pretty good yes, I’d say it even exceeds the VT-4 in some regards, if that’s what you want to refer to as the “core”, but credit for that goes to the Russians. Everything else in a tank needs to be upgraded with time, even the most basic of elements.
Take a look at Russian T90 tanks and then Indian T90 tanks. Russian ones have 3rd Gen ERA, Indian ones have second gen, with no plans to upgrade it anytime soon (considering the new ones being produced still have 2nd Gen K-5 ERA). Pakistani tanks use FY4, Nozh and Aorak 2 (all three are third Gen ERA). The last Pakistani tanks to use K-5 2nd Gen ERA were T80UDs and even those have Nozh now.
Russian tanks use third Gen thermals, So do AKs and VT-4s, Pakistan stopped putting Catherine FC in new tanks in 2013. The new Indian T90S being produced is still getting Catherine FC (which is a second Gen thermal. AK had this same thermal when it started production in 2000s, Indian T90S has it in 2021.)
VT-4 is superior to T90S in every single metric, armor, penetration, mobility, Technology (it is currently the only tank in South Asia to have a CITV system, which is a Huge upgrade. Not to mention it has a functioning hard kill APS. CITV and APS are the two most important upgrades for modern tanks, it’s the only tank in south Asia to have both.) it has 1500HP modular engine compared to older style 1000HP in T90S. It has 8 digital panels, 4 for commander, 2 for gunner, 2 for driver, compared to 2 or 3 in Indian T90. It is a generation ahead in Thermals, ERA and Ammunition, and most of this applies to Al-Khalid-1 too. Not just the VT-4, as the AK-1 and VT-4 are rather closely matched in physical metrics.
The Latest Chinese and Russian APFSDS rounds have penetration numbers in excess of 800MM/0 Deg at 2KM. Pakistan uses Naiza and BTA-4, with 600 and 650MM/0 Deg at 2KM. India started buying BM42 Mango APFSDS in 2019 (
https://zeenews.india.com/india/ind...mango-shells-for-t-72-t-90-tanks-2138461.html) which came into service in the Soviet Union in the Mid 80s (has 460MM/0 Deg at 2KM) which would mean a lot of Indian tanks still use older ammo. Pakistan was producing its own APFSDS-T in 2003 with penetration numbers similar to that.
Keep in mind only half of Indian T72 fleet is modernized and is able to use this already ancient ammo. The other half will have to use even older ammo that likely cannot even penetrate a Type 69s turret.
India has number advantages yes, but on average the Pakistani tank fleet is far more modernized. Al-Zarrar fires the same ammunition and has the same ERA as Al-Khalid. It has second Gen thermals as well. That means even Al-zarrar has superior fire-power and similar optics than Indian T90S.
Al-Khalid has IBMS as standard since 2000s. It was developed in Pakistan. VT-4 has had Trophy-like hard kill APS since 2017, it also has IBMS.