The phrase "a complete natural" is correct and usable in written English.
It is typically used to describe someone who is very skilled or talented at something without needing to try hard or learn formally.
Example: "When it comes to playing the piano, she is a complete natural; she can play any song by ear."
Alternatives: "a born talent" or "a natural talent".
He was a complete natural.
By contrast, Bale, all pumped up and preening, took to the job like a complete natural, as if this was what he did in his downtime.
She went away and spent six months working on her voice, in between other jobs, and it was just … like everything else, she's just a complete natural.
Real-time streaming seems a complete, natural fit for what they're doing with Stories.
Results are fairly promising to reach a stable core cooling system based on a complete natural convection.
These three families of natural mode shapes form a complete natural frequency spectrum of a free rectangular plate as a novelty.
We conducted a cross-sectional analysis of data from the Boston Osteoarthritis of the Knee Study (BOKS) [ 22] – a completed natural history study of knee OA.
A completed, natural-looking breast can provide any breast cancer survivor the confidence, self-esteem and comfort that she deserves.
Even Alan Shearer, before his late career habit of spending most of his time wrestling his way backwards across the halfway line with his arms stretched out, like a man reaching for the mantelpiece after a power cut, was in his pomp a wonderfully complete, natural, modern centre-forward.
ASL is a linguistically complete, natural language, and signed languages have developed organically in schools for the deaf, even when these languages were being actively suppressed in favor of "traditional" forms of speech.
Compiling a more complete natural history of back pain across the life course would be helpful, and perhaps improvements in the collection of history might help, beyond whether someone has experienced back pain in the recent past, or in their lifetime.
