I think the lesson to draw from bigorgs isn't what to as a smallorg, but what directions you can grow and what the pitfalls are on those roads.
Any smallorg probably wants a bare monorepo, git or what have you. If you grow to the point that becomes unwieldy, you can either invest in tooling the way Google has, or be prepared to split the repo into library and project repos in a way that makes sense for what your mediumorg has grown into.
Google is a monorepo with sixteen layers of tooling to make it searchable, to not require you to spent 3 days making a local copy before editing, to manage permissions across orgs, etc etc etc.
A small organization of 1-20 people should not emulate the layers of tooling; just have a single git repo somewhere and call it a day.
Any smallorg probably wants a bare monorepo, git or what have you. If you grow to the point that becomes unwieldy, you can either invest in tooling the way Google has, or be prepared to split the repo into library and project repos in a way that makes sense for what your mediumorg has grown into.