India’s navy is still orders of magnitude below the standard of the modern Chinese fleet, and their doctrine is outdated in modern naval warfare

This assumes that things remain the same for the foreseeable future. If WW3 starts and finishes by the end of the decade, I would agree with this point. However, it is difficult to imagine that India will make no headway in military modernisation by 2030, especially if it has plans to participate in hostilities against China.

Not to mention, in a collaboration scenario, the west can help india speed up modernisation (and it will have its own internal initiative as well)

Also, their land borders with China are all nearly impassable Himalayan mountains and narrow passes,

They don’t need to conquer China through the himalayas. They just need to occupy Chinese efforts and attention.

the least capable major power in the world militarily relative to other similarly sized countries

The only country with a similar size is China.