I have not seen many cases where growing the team and product made the code base less sloppy 
But our reality is a bit trickier.
Beeing an ERP System there are many different parts for the user to be presented. And almost all of them share the same data classes.
If we were to split it, it would proboably result in one data_core dependency and about 10 “UI” Apps which all depend on the datacore.
New features will most likely need changes in the data_core app and some change on a “UI” app.
We are currently 4 Engineers, and I do not see a way we could continue to implement features in such a setup. Because the “UI” app either depends on the master wich would result in chaos if 4 peopel merge in paralell while developing. Or on a specific version wich would be very tedious to debug new features.
Unless I am overlooking something at least at the moment we can’t split our codebase.