I think the biggest issue is dealing with very large code bases, like the code for a mid-large size company. You either go with a monorepo and deal with slowness, Windows-only optimizations and bare minimum partial checkout support.

Or you go with submodules and then you have even bigger problems. Honestly I’m not sure there’s really an answer for this with Git currently.

The partial checkout support in Git is getting improved. Take a look, maybe it now solves your problems.

Support for large repositories via scalar works also for Linux (though not everything is ported; as main body of work on supporting large repositories was created to deal with the size of MS Windows repository, it started with Windows-only support / optimization first).

There are alternatives to submodules, like https://github.com/chronoxor/gil