Micro-services is about partitioning based on functionality and features -- so I think more often than not, 99% of the microservices use 10% of the storage and 1 microservice use 90% of the storage, and you're back to solving the problem of horizontally scaling your storage regardless of microservice vs monolith.
thats sometimes true, not always. but a good observation. Even if it is true, having that 90% usecase behind its own service often allows a lot more flexibility to scale for that particular storage problem , and not have to use it generically/everywhere. Eg, time-partioning, cold archiving, sharding, whatever is suitable for just that use case.
