Yeah it's preatty interesting question. In this regard India is similiar to... Soviet Union and it's completely absurdal situation where 3 design bureaus were designing 3 MBT's for Soviet Armed Forces that were manufactured in more or less the same time, and were not share common components... incredible logistics nightmare.
In India situation is preatty much the same, we have low quality T-72M1 as most numerous tank and two high quality tanks in smaller numbers (T-90S and Arjun), similiar situation as in Soviet Union where there were two high quality tanks, the T-64 and T-80, and a lower quality tank the T-72.
Similiar situation is in China, where there is low quality tank the ZTZ-96, and high quality tank ZTZ-99.
While most other countries try or were able to achieve one MBT fleet (although with different variants that at least share spare parts commonality).
USA - ~8,000+ M1/M1A1/M1A2 tanks fleet.
UK - ~300+ FV4034 Challenger 2 tanks fleet (although in early to late 1990's there were also FV4211 Chieftain and FV4030/4 Challenger 1 tanks in the fleet).
Germany - ~200-300+ Leopard 2 tanks fleet (A5 and A6 variants in active fleet and A4 in reserve/training units).
France - ~300-400+ Leclerc tanks fleet (Serie II and Serie III/XXI in active fleet and Serie I in reserve storage).
Italy - ~200 C1 Ariete tanks fleet.
Other NATO countries have tank fleets with more machines of various types, because of nececity or other reasons but the long term goal is to achieve one type tank fleet if possible.
Russia also have many tanks but this is a legacy of Soviet Union, but the main goals are:
1) Start production of "Armata" heavy tracked platform and new MBT based on it.
2) T-72 and T-90 series are most wide spread MBT's. Both share some parts commonality.
3) T-80 series used until spare parts will end, then all will be scrapped.
4) T-64 series retired and slowly scrapped.
5) T-54/55 and T-62 series scrapped.
6) Other unusuall and old tank types retired and mostly scrapped.
Primary reason would be terrain. Secondary will be the supposed acquisition of Abrams by Pakistan in the late 80's, hence a 60 tonne Arjun.
Terrain.
1) Kashmir - Home to some of the highest mountains in the world.
Operation Bison (Jammu & Kashmir 1948) - Wikipedia, the free encyclopedia
2) Punjab - Plain but has a maze of canals on both side of the border. Very high population density.
3) Rajasthan - Thar desert.
4) Gujrat - Desert, semi desert and salt marsh.
Many countries have similiar variety of environments and use one type of MBT. IMHO if there are problems with vehicle weight and infrastructure, the best solution of India would be T-90S or eventually more modern T-90MS, it's weight is less than 50 tons so there would not be so big strain on infrastructure, and T-90S is well suited to counter both Pakistani T-80UD, Al Khalid as well as Chinese ZTZ-96 and ZTZ-99.
On the other hand heavier vehicles are operated by other nations in similiar environments and there are no big problems with infrastructure, US for example have not only temperate climate regions but also arctic or desert ones (also with mountain regions) and have armor-mechanized units stationing in such regions without problems, and the overall trend is to make vehicles better protected (this also means that these vehicles will be heavier).
So it is certainly good question if India needs so many MBT's of 3 various types without spare parts commonality, that makes use of them more expensive and adds stress for logistics chain.
you are in ballpark range
