I'm not sure what they've been left with is a monolith after all. I would say they just have a new service, which is the size of what they should have originally attempted before splitting.
In particular, as to their original problem, the shared library seems to be the main source of pain and that isn't technically solved by a monolith, along with not following the basic rule of services "put together first, split later".
I feel prematurely splitting services like that is bound to have issues unless they have 100 developers for 100 services.
The claim of "1 superstar" is misleading too, this service doesn't include the logic for their API, Admin, Billing, User storage etc etc, it's still a service, one of a few that make up Segment in totality.
In particular, as to their original problem, the shared library seems to be the main source of pain and that isn't technically solved by a monolith, along with not following the basic rule of services "put together first, split later".
I feel prematurely splitting services like that is bound to have issues unless they have 100 developers for 100 services.
The claim of "1 superstar" is misleading too, this service doesn't include the logic for their API, Admin, Billing, User storage etc etc, it's still a service, one of a few that make up Segment in totality.