What you are describing is exactly what I meant by old legacy Zope2
applications.

You should be able to use this style of development with Zope 2.13.
But you won't be able to upgrade to newer versions of Zope 2 anymore
and expect your code to work unmodified. We discouraged this style of
development for the past six years. It should come as no surprise that
it will come to an end at some point.