Eh...Yeah. People would pay tons of money to get a useless ornamental sword fused with a gun instead of an ornamental sword AND an ornamental gun both of which COULD be used...
Yes, they probably were not much of a gun (only one of those shown on the photos was a "revolver"), but that doesn't mean they weren't used because of being unwieldy. It just means that before the technology grew high enough to make it viable, guns increased so much in their utility that the melee element was no longer needed beyond a simple bayonet.
Gun-sword is a MELEE weapon that can help shooting that guy few meters in front of you before he shoots you. A rifle with bayonet is a ranged weapon that can be used in melee. And since ALL melee weapons in warfare went the way of dinosaurs eventually (with exception of daggers/knives) as guns were developed, it's pretty obvious that the purpose of a gun-blade simply was not needed before the technology could make it better and cheaper to make. You know...weapons, guns especially, never were cheap or easy to make in the times of swords.
Also, arguments about it being unwieldy are born from a poor design of them in game, not from reality. There is absolutely no reason why a short sword could not have a gun handle...and that's the only real change. The "gun" part is where the hilt normally is, so extra weight is added at the point of hand. And that's nothing that cannot be counteracted with weight on the other side of the handle. Like it was done for normal swords too. Well represented by the long one that is on the second photo.
Katars are held much like a gunblade would, and yet they existed and were pretty widely used (and there were ones well-suited for slashing attacks). And I dare say that a gun-sword would be a piercing weapon more than anything anyway in reality.
Balance is based on material density and distribution. There were tons of low-quality swords that were poorly balanced and were unwieldy, just because the smith didn't know any better.
So there is no reason why an ergonomically sound gun-blade could not be made.
That being said... this exists. And yes, that is a blue mage. With a gun. Not a gun-blade, a gun.