Just because you make a total conversion, add a few mechanics to a game, does not classify it as its own game. There are things you simply cant change. For example: source engine bullet mechanics, physics, hit registration, net code.
But we've gone way off topic at this point.
Hacking, exploits, whatever anyone wants to call it needs to be fixed, unity engine or not.
Yes way off topic but just so you know The bullet mechanics do vary from game to game for example bullet pen even physics vary slightly. But your right about hit registration (like hitscan) and netcode. Your last point I completely agree with if course :)
We could prob argue the source thing for ages though with no real end in sight lol so enough on that