> For example, everyone says you can 'use SQLAlchemy' in Django. On paper this is true. But then you lose the admin, the user auth system, the messages system, model forms, and all of the other batteries that make Django useful.

Using SQLAlchemy doesn't change any of that. For pre-built components, like auth and admin, just go with the flow. You're free to use SQLAlchemy side-by-side with Django's ORM.