Oh yes, the KADA-4 is almost inordinately heavy. However, it is also designated as a heavy rifle. Heavy weapons like the KADA-4 are meant to be carried by armored assault troops, wearing servo-assisted combat armor, such as the venerable NDC Archons. Even basic security/light infantry armors are often compatible with a shoulder-spanning rig that affords limited additional lifting/throwing power. NDC grenadiers carry an exoskeleton device just simply for this purpose, affording them extra throwing range. The harness resembles a backpack connected to a pair of armored pauldrons and gauntlets, with an estimated maximum lift weight of 80 lbs. When worn by a human, this complements the wearer's initial lifting ability, whatever that may be.
Though odd in design and size, the KADA-4 is gyroscopically stabilized, intensely reducing the gun's powerful kickback and enabling precise concentrated fire even when held without bracing. The stock does not extend; rather, it pivots either to the left or to the right for bracing against the user's hip or combat belt. The KADA-4 is carried by NDC Archon squadrons as their primary weapon, perfectly matched with the lifting power and dexterity of their assistive armor.
The KADA-4 can also be easily rack-mounted, affording it utility as an anchored heavy machine gun.
Basically, the gun is meant to be braced against the hip for better center-of-gravity stability, and targeting systems linked to the user's helmet or headset afford them the same sighting power as a traditional "iron sight" system. Think about something like the heavy pulse rifle from Aliens.