If I remember correctly, he shot a small target from, like, a continent's distance away, survived being shot and turned into swiss cheese, survives anything thrown at him (including if you choose to shoot at him when it's revealed you're an undercover cop) and more that I'm probably forgetting (it's been a long time since I last read Breach)
The parts where Gabriel meets old acquaintances and talks to them as if he's known them for 100 years make you feel like the side-side-side character. Though for some reason I don't mind it as much as I do in Tale of Heroes where the MC is also the side character (probably because you can get cucked. At least in Breach the mute character that has a crush on Gabriel will start loving you for real if you romance her. AND because the self insert in ATOH is insufferable, Gabriel is at least funny.). At this point I wouldn't be surprised if the author revealed Gabriel is literally archangel gabriel sent by god to be a gangster.