It is BOTH. That's what drew me to this in the first place. This shouldn't be one against the other. It's like music. There are lots of mathematics and theory behind it, and the more you know, the better you can create. But when you focus too much on mathematics and theory, you lose the art. Brewing without science is blind art (like slapping paint on a wall and calling it art). Brewing without art is too scientific.
All these questions we have... attenuation, head retention, bitterness, infections, sanitization, etc.... it's all science. And knowing how and why these things occur makes us better artists. You could fit an array of science into brewing... microbiology, physics, mathematics, chemistry, etc. The more we understand these (without being too caught up in them), the better artists we are. To me, brewing science leads to brewing art.