Big monolithic repos actually increase the mental complexity more in our opinion. Mental complexity really comes with how much of the system you're holding in your head at once. And with smaller repos you might be dealing with 10-20 repos on any given day, but that's only 1-2% of our codebase/system. The other 98% is ignorable. So we end up holding less in our heads, assuming we've abstracted things correctly.
It did get annoying to deal with the mechanics of lots of repos. So we built tooling to make that easier. For example, CLI commands like "goto analytics.js" will clone and take us to the local copy of the repo. And "publish patch" handles all the mechanics of updating History.md from the git log, incrementing the version appropriately in package.json and component.json, tagging the commit and releasing to github and npm. Khaos, also mentioned in Sperandio's article, helps us template out new repos quickly. With a few pieces of tooling like that you can move pretty fast across lots of repos.
It did get annoying to deal with the mechanics of lots of repos. So we built tooling to make that easier. For example, CLI commands like "goto analytics.js" will clone and take us to the local copy of the repo. And "publish patch" handles all the mechanics of updating History.md from the git log, incrementing the version appropriately in package.json and component.json, tagging the commit and releasing to github and npm. Khaos, also mentioned in Sperandio's article, helps us template out new repos quickly. With a few pieces of tooling like that you can move pretty fast across lots of repos.