It's not like we're getting newer versions like T-90M/MS. So there's no comparison between the two in terms of armour, firepower as has been amply proven during comparative trials some time back. Russia reportedly diverted some T-90S meant for India to Ukraine and we've all seen what happened to those.
As for maintenance, and logistics, this tank has been in service in numbers for nearly 25 years. Painstaking effort has gone into customization- including indigenous AC units, tank barrels, even armour panels - all tech spin-offs from Arjun. The Russians refused to part with ToT for key items. We didn't even buy Shtora APS to keep costs down.
Imo, there's nothing the T-90S has today (including the so-called Mk3 version shown recently) that an upgraded T-72 MKI wouldn't have brought to the table.
We decided to skip on T-90MS, instead chose a more modest upgrade.
T-72 can be upgraded T-90 standards in some ways, but the turret will have to be replaced, including autoloader, armor, gun, and barrel. Not worth the dough, that's why we decided to skip on T-90MS too.