Thanks @fredrikekre. I think by this:
devthem all at once instead.
you mean dev PkgA PkgB, no? If so, that’s not really getting at the problem. The point is that PkgC now has to dev all of the local dependencies for every package it uses, which is hard to maintain. That is, if you add a new dependence to A, you have to go add it to anything that uses A, and to anything that uses anything that uses A, etc., which is clearly a big mess.