There are no 'self defence guns'. As I have said elsewhere, a bulletproof vest is what you need if your objective is self defence.
Keeping saying so doesn't make it reality.
A bulletproof vest simply gives you a better chance when lead is heading your way. If you can't shoot back it's basically worthless. (Note: In protection situations you often see vests on unarmed people--but they have guards that can shoot back.)
A gun only works offensively; it can defend you against another person's gun only if used preemptively.
So? Self defense does not require you wait until they have actually used a weapon on you. The threat is enough. Real world, here, a few years ago: A woman wakes up to find her stalkerish ex in her bedroom. Said ex is now 6 feet under.
Real world, someone I used to know who carried a gun when doing yardwork. The neighbors had an aggressive dog, it had already bitten him once. If the dog came for him it would have been perforated. The neighbors finally got serious about containing the dog, he never had to shoot. There would have been no obligation to wait for the dog to bite before shooting.
Standoffs are for movies. In real life, the first to fire wins, so there's no motive not to shoot first.
Where's the defence? If someone knows you are armed, he knows he must kill you to defend himself against you.
In a lawful self defense situation he can surrender or run away.
In a fistfight, the first person to throw a punch is in the wrong, and landing the second punch is (in most jurisdictions) considered reasonable self defence.
You cannot assume that you will be around to fire the second shot in a gunfight. Guns are not defensive weapons, and pretending that they are has caused more than enough grief in America.
1) Your scenario moves the goalposts. You are equating throwing a punch and landing a punch. The last time someone threw a punch at me I stepped backwards, they only hit air. I could legally have hit back, though--and I would have been the first one to land a punch. (As it was, he was controlled by others, I took no action.)
2) The law doesn't require that you actually be attacked in order to defend yourself. Threatened is enough.
It's time to grow up and stop pretending.
You're the one that's pretending.