At the factory, they pack the bearings correctly and don't bother with trying to fill the entire system with grease. So, there's a lot of air to displace. Plus, there's all that grease that gets pushed past the seal and is now contaminating your brakes.
Seriously, to even attempt using a super-lube type system, you need to get the axles and hubs really warm (drive around dragging the brakes), let the grease cartridge sit in a bucket of really hot water for a half hour, then pump it in very slowly while spinning the wheel/hub. Otherwise, you're probably contaminating the brakes and making it a bigger job than just doing a hand repack in the first place. But, if it's time for the bearings to get new grease, then they also need to be inspected, which can't happen unless you take stuff apart.
Super-lube systems are a gimmick for anything except a boat trailer.