I give you a very fine example of what I mean by saying that Michelangelo considered himself a sculptor. Here is one of the images which he painted on the Sistine Chapel.
This is the Lybian Sibyl, a priestess who was also the daughter of Zeus (remember, the Renaissance is back to Greco-Roman ideals). It's a marvelous rendering, but don't you notice that that does not look very much like a woman's back? It's way too muscular and wide. This is so for two reasons, the first and most obvious being that women were not allowed in studios at that time, not even as models, so Michelangelo had to do his best looking only at men. The other reason for the overly-muscular appearance of this figure comes from Michelangelo's identity as a sculptor, using light and shadow also in his paintings to make the image look three-dimensional and alive. Here was his study for the above fresco.
Only a sculptor makes such precise body parts.