As I see it (and I haven't been convinced otherwise), the only advantage microservices have over monoliths is that they can scale horizontally more easily, and a slight advantage is that they pressure you to write cleaner interfaces.

There's nothing preventing a monolith from being as modular as a microservices architecture, only without all the headaches that come with monitoring tens of services and sticking a network between them. There is NOT just as much complexity in a monolith, because you have no network of services to monitor, there's only one service.

Sure, your business logic is going to be the same in either approach, but you're comparing badly written monoliths to well-written microservices. There's nothing that says microservices can't be a mess (and I've seen multiple people completely botch it and have all the services talk to the same database).