Annual is arbitrary since it's a random fact of earth. If nothing else changed except we just happened to have a 6 month year, then GDP is half, and comparisons of that rate to an amount would now be completely different.

Comparing them is like comparing gallons as a number and speed of a car as a number, and ignoring that speed in mph or km/h or m/s will give different answers. Sure there are relations, but they're not comparable as ratios.