The main benefit most people see right away is the Pydantic integration & it requires less boiler plate for basic API's. Ninja is essentially FastAPI + Django.
I prefer Ninja over DRF, but I know plenty of orgs who still love their class based DRF views as once you are over the (significant) mental hurdle of understanding all the abstraction there, it does give you the common CRUD type operations on your models "for free".
DRF has more abstraction. When I was new to Django I found DRF hard to build a larger API with it and not make mistakes or have things get confusing. You're primarily working by extending classes etc.
With django-ninja you just define your APIs with annotated types as methods, there is no magic, and then you get a generated OpenAPI spec.
this was my experience anyway, I used DRF for this project [0] and ninja for this one [1]
I haven't used django-ninja but to me it looks like the API is a bit nicer or more 'modern' looking (i.e. declarative via type annotations) and it's faster, both due to being based on Pydantic
DRF is old and API looks more like Django forms or class-based views, more of an OOP hierarchy going on, and DRF serializers are slow
Old is a harsh word, maybe mature would be a better fit, not everything new and shiny is gold, and yet not everything old sucks.
Not arguing here about types and Pydantic being faster than the built in ModelSerializers. However, for serializer speed improvements and performance in DRF I would advise dropping ModelSerializers and either going for Serializers or plain dict. Haki Benita has a beautiful article on that [0]. I was able to accomplish sub 200 response times on a fairly large response from tables that had tens of millions of records.
I think you have no objective reason other than your styling and rather personal preference for function based views?
[1] https://django-ninja.dev