How to choose the correct fuse in a double paralled battery supply system?
Use a circuit breaker link:

As you see, it can trigger in less than 10s when beyond nominal current.

As you said, 200A nominal current. When short circuit you get 1.6kA. 833A per battery, the 200A breaker resistance is 1.2 mohm. It will trip in 50ms (800% overload), the fuses would survive since it would take 2s to blow them.