The problem is not when you need to change the implementation of a module, it's when you need to move the boundaries between them. What you are describing is a

The problem is not when you need to change the implementation of a module, it's when you need to move the boundaries between them. What you are describing is a reasonable approach if you can get the module boundaries right in advance. For more open ended software problems, that is impossible - you need the freedom to rearchitect and change responsibilities. That's the situation where a monorepo is much simpler than anything else.