I have never found either (1) or (2) to be a problem in hundreds of thousands of lines of Python.

> In particular, C3's "path shortening" ... we'd have to pay by actually writing `std.io.file.open("foo.txt")` or change to a flat module system.

You can easily and explicitly shorten paths in other languages. For example, in Python "from mypackage.mysubpackage import mymodule; mymodule.myfunc()"

Python even gracefully handles name collisions by allowing you to change the name of the local alias, e.g. "from my_other_package.mysubpackage import mymodule as other_module"

I find the "from .. import" to be really handy to understand touchpoints for other modules, and it is not very verbose, because you can have a comma-separated list of things that you are aliasing into the current namespace.

(You can also use "from some_module import *" to bring everything in, which is highly useful for exploratory programming but is an anti-pattern for production software.)