That's not foolproof either.. though I did it for many years as well.
Lately, I find that it is a much better practice, and a financial profit center to insist on the camera being audio backup, and a separate recording being done on a standalone recorder.
Also, why are people accepting one man band bookings on anything with a pro camera? You are cheapening your results, and making yourself work harder.
I mean, I can understand shooting an establishing shot or 2 by yourself, but better results come from having support in light, sound, and data management.. not to say of freeing you to manage client relations.
Millions of man years of film, tv, and video produciton in the professional arena might not be wrong....
Does sound recorded separately sound better? The answer is yes. It sounds better because the audio recording capability on Epic/Scarlet is simply not as good as it should be.
We are not cutting corners, we use a dedicated sound recordist BUT having to sync up sep sound is a pain, takes time and ultimately that costs us money. Just because the film industry has always done it this way, does not mean that this is the way we should be doing things now.
Compromises were made when designing Epic and Scarlet and the audio side has suffered. Feedback like this is important for RED and will allow them to make better products - Jim's quest is to make the best camera in the world, the pictures are nearly there, the audio however needs work.