That's a great question. I mean ability to serve concurrent requests, or throughput. Microservices will typically worsen other metrics like individual response time.
I am not sure microservices are good for scalability in that sense. Microservices divide your application vertically, but for scalability you want to divide it horizontally. You don't want a separate service for each feature of your app, you want an application server that you can replicate as many times as necessary.
Microservices can scale both directions, same as other systems. You can allocate more resources to individual service instances (vertical), and you can allocate more service instances (horizontal). The later scaling should be done in an automated fashion.
If you look at something like Spring Boot, you will find that an individual service instance is a stand-alone application server. That is what is duplicated when a new service instance is created.
