Internationally things don't work this easily. It's more like a quid pro quo system that works when it comes to international data sharing. So if they want to gather data from international exchanges they obviously need to offer their data to these countries government as well. You cannot enforce this on them, also the threats of banning them might not also work because India isn't a very big market for them anyway.
Secondly, I am very sure this isn't to solve the crime committed using cryptos. NO ONE commits a crime using crypto and sweeps the money to a CEX. This is more to find about tax evasions and ensure tax compliance of 30% tax which the government has kept.
But as you said getting it from Tax haven exchanges would be like an impossible task for sure.
Knowing the current government and its foreign policy it is possible that data-sharing between the governments would be the primary way to get user data on CEX. Getting Indian user's data would be the primary motive as it does not make sense to ask CEX for user data. If someone wants to commit a crime they will always use a DEX to sweep their money. It is far more convenient for a criminal as they can hide their identity.