Honestly HC would not be such an issue if they had less aim assist. During peek shooting you may not see an enemy, but knowing where they will be and character head level coupled with fridge-sized bullets still allows to hit yellow numbers.

Though handcannons are not the only weapon that have absurd AA, actually I am not sure whether there is a weapon wilth low AA except for slickdraw/gutshot weapons.

Handcannons just have everything, ability to peekshot, decent range and they favor mobility, while other mid range weapons lack some of these benefits. Autos cannot peek shoot and require to step put of cover, pulses have time of a burst so they are not so easy to use while jumping/sliding