On flat roads, air resistance is the biggest force a cyclist has to overcome, and the rider’s body creates most of it. That makes position a powerful lever, even for amateurs.
At typical speeds above roughly 30 km/h on the flat, aerodynamic drag makes up the large majority of total resistance
Lowering the torso and narrowing the arms often saves more than expensive equipment changes
An aggressive position is only useful if you can hold it and still produce power; comfort and sustainability matter
On steep climbs, speeds are lower and weight matters more than aerodynamics
A cheap test: on a calm day, ride the same flat out-and-back route at the same power in two positions, for example hoods versus drops or a narrower aero bar setup. Repeat a few times. Consistent speed differences at equal power give you a rough idea of the gain.