It's mostly his core that puts Genos--and Kuseno--SEVERAL leagues beyond what we or anyone else has IRL or in the series, at least that we've seen. It's a completely stable nuclear reactor that can withstand massive trauma, that can fit in the palm of your hand, be transfered safely between systems, and doesn't cause radiation poisoning. It would be one of those world-changing innovations if it actually existed. Could you imagine if suddenly everyone had that much free power at their disposal? Like look what happened when steam engines hopped off.

I think the design is based on the Advanced Inertial Reference Sphere, and the demon core. One is a marvel of engineering, and the other was a radioactive nightmare because of a slip of a hand.

It's genuinely shocking Genos hasn't been raided for parts yet, by anyone we know. Drive Knight was eyeing him up for good reason. I think Genos' firepower is as much to protect himself (and Kuseno) as it's meant to help him fight.

((Edit to add--and this says nothing of the fact that Kuseno made a hyper mobile life support system that can withstand EXTREME heat and physical abuse without causing any damage to the most delicate organ in the human body, that's also relatively easy to reconstruct, all things considered. He's got SO MUCH SHIT other people would kill for. There's lots of reasons for him to stay hidden at all times ><))