This idea sounds great, until you come up against the realities of organizations that also demand "agile" methodology.

Projects are typically organized with cross-functional teams that have to negotiate project requirements, timelines, and produce deliverables in an iterative manner. The idea that you have a single team leader who is responsible for a single thing sounds great -- if that person gets to pick each member of the team and the team is also responsible for that single thing. you are pulling together teams who report to different people/organizations and who probably are themselves assigned to multiple projects.

If the STL doesn't get to pick the team, or if the team isn't also singularly aligned with a single business focus, you have a situation where the person primarily responsible for an initiative is essentially competing with their team for time. And that STL probably is not empowered to demand cycles from their team because the resources are cross-functional and report to other people, so you need to work with your project manager to get more time for your resources. It can be helpful to eliminate a question of who the "product owner" is, but that product owner is likely to be placed in the unenviable position of getting sandwiched between the business leadership demanding results and teams who have shared responsibilities and who don't actually directly report to the STL.

In short -- whether an organization is large or small, this model is a very good way to find scapegoats for when projects go wrong, but success depends on the organization committing people and technology to a problem rather than a single leader.

This sounds like a great idea at Amazon's current scale, but I struggle to see how this is possible at a company with <20 head count. There are so many different areas that need attention when running a business, and many of them require less than one person's full time.

...Maybe the move is to bring process-driven management to the startup. You outsource all non-core processes, including payroll, benefits, invoicing, accounting, legal, HR, finance, etc. You could then have an eng leader, a product leader, a sales leader, a customer success leader, and a "vision" leader. Sounds like a lot of the VC backed startup world, actually.

...but at that scale, each "single thread" contains multitudes. In "engineering," there's recruiting, mentorship, internal tooling, existing process maintenance, new project scoping & architecture, sprint planning and execution, the list goes on. So the "single-threaded" eng leader is actually multi-threaded across all these different sub-areas.

The single threaded leader is multitasking among their various teams!