SQLAlchemy is way more complex and does more stuff (more robust connection pooling for example). There are a lot more complex things you can do with prefetching related rows with SQLAlchemy (there’s like 5+ different ways to do it?).
You’ve actually used sql alchemy for a project? It’s great, I just wouldn’t describe it as simpler.
Maybe “less opinionated” is what I’m getting at; it has smaller, more composable building blocks and while the ORM API surface itself is in some sense more complex, it doesn’t have the kitchen sink of ActiveRecord integration that Django does. It seems to me that when you pick an implementation, you perhaps have a little more boilerplate than Django, and then the slice of the SQLAlchemy API you end up using is smaller and more explicit. So the app’s usage of the ORM ends up being simpler (even though you might have to write a little bit of framework code yourself).
(Yes, I’ve used both, Django more though.)