The most common alternative to organizing teams by service boundaries is to organize teams around the business problems to be solved. That is a lot easier to budget for than trying to staff by microservice boundary, doesn't have the coordination and planning overhead, and it means you aren't reliant on up-front planning to get to a functional solution or design.

In high-uncertainty greenfield development, Explore projects or Lean Startup-style experimentation, having developer be close to the users they are serving is very efficient.

It also lets those companies reteam frequently, without needing to change the software to match the new team boundaries, which is very helpful when growing the team.