I think that's two ways of saying the same thing - that NetBox isn't integrated into anything which forces it into being the source of truth. It's just a place updates sometimes get sent to.
Your ansible (salt, chef, whatever) inventories should be generated from your source of truth, then when they run they should apply against your infrastructure.
You shouldn’t be able to make any changes without driving them through the source of truth.
This is great if your source of truth can be NetBox alone but if NetBox is just a destination for generated workflows relying on things like actual DDI, which is what's actually required for the workflow, as the source of truth the idea every one will remember to update and cleanup NetBox falls apart.
Not to mention not every place can be assumed to declare their entire infrastructure in ansible chef or whathaveyou. If IT people everywhere got the time to redeploy their entire infrastructures only with what works for best practices to make their lives easier then IT people would probably be a lot happier :).
This was my main problem with NetBox as well.