I'm now retired primary care nurse but I did it for 23 years and never stopped training. In some areas of care I had more training than the GPs who employed me and they referred patients to me.
There were several instances where I added tests and managed to get patients an earlier diagnosis of cancer. I would communicate with hospital consultants and suggest treatments or collate information between two different departments where one condition was being ignored over the need for consideration of another. I also shared some patient care on respiratory conditions with a nurse consultant who the GPs referred to
However, there would be a core of symptoms we nurses would always refer to a medical professional.
I've even had patients ask why had their GP not explained this before, or they wish they had seen me sooner.
Conclusion is obviously training is important as is being qualified, but in my observation it isn't just that alone and being good at one's job is more than academic level but application of knowledge, nuance, gut feeling, "knowing what you don't know", emotional intelligence, motivation, good communication, etc etc.