this is becoming less true with every generation of model.
a decent model with a decent harness will determine when the knowledge base is lacking and attempt to fill the holes; thus the good general models can be very easily brought up to speed on niche domains.
You're thinking like an engineer.
Think like a regulator.
Ugh? It is not just the knowledge
Some model are more aggressive by default, some are more verbose by default. To get the result you want for your specific application, you run experiment with prompts and parameters.