Inserts very slow near the end of dataset
You have run out of resources! 

With 202M records, even one record would be only 64 bytes (you can check with db.collection.stats().avgObjSize), the size is 12GB and then comes index. The optimal situation is when active data, (index and data) is in the memory. This case it is NOT. So, mongod starts using disk heavily and if your disk is not high IOPS (SSD base) and low latency base, your machine starts slowing down.

Can you (for start) increase memory to (at least) 16 - 32GB?