Open source is supposed to be a community. Forcing a breaking change like this on all their dependencies that they could have avoided with a one-line import statement is, IMO, not very good behavior as a community member.
No one is forcing a breaking change on anyone.
a) PIP usually retains past versions
b) A python package can specify it's dependencies, including their version, as hard requirements
c) virtualenvs exist
If he doesn't do that, and instead specifies only `some_dependency`, that signals to the package management software that the package works with the `@latest` version of that dependency. The onus to make sure that is, and continues to be, the case in code, is on the maintainer of the package, not the maintainer of the dependency, period.
And no, this is not "disrespectful". This doesn't go against any sense of community in FOSS. This is established practice in software development and package maintenance.