You're right that World Tour pros have probably spent more WT time than Hammer, but worth noting that road TTs and Ironman are very different events than an IP or TP. The only thing they have in common (literally) is aerobars and a stopwatch.
Hammer's arms aren't wider than her thighs. Her hips are wider than her shoulders, and her arms don't go *out* from her shoulders. They're in line
As bitingduck pointed out, most aerodynamic doesn't necessarily mean fastest. Most Speed might sacrifice some aerodynamics for power, and the shorter the TT the more important maintaining the utmost power output is.
Of course, we could be talking in circles, or saying the same thing from opposite directions. Maybe it's for stability in turns - and maybe that's where they get power from.