Whereas the actual buckler was invented specifically to get around the rule that donning or doffing a shield requires an action, since it is carried, drawn, and wielded just like a sword. A small, blunt, pancake-shaped sword. So don't knock inventions for getting around rules. Real people do it too.
But yeah, I tend to assume that any hands-free protective gear like a vambrace is included in your Armor Class by default as part of, y'know, your armor. "Can I strap a shield to my chest and get +2 AC for blocking with that?" "That's called a breastplate."
Well, no not really. That has nothing to do with why the buckler was invented. Any round shield with a boss (the metal half-sphere that sticks out of the front) was wielded by a handle that goes across the middle of the boss on the back. The method of using such a shield, was to simply pick it up, and then you "punched" at the incoming attack to deflect it. Those types of shields typically didn't have guige straps that were used to strap it to your back, although a targe (a round shield without a boss and utilizing straps - one over the forearm and the second to hold with your hand) might. But shields with a boss are older and are very quick to just grab and go.
More importantly, though, the amount of time it took to don armor or grab a shield were also irrelevant. War was a prepared thing, with plenty of time to prepare on your side of the battlefield. It would have been very rare for somebody to worry about whether it took 2 seconds or 15 seconds to prepare their shield. Just like it didn't usually matter that it could take as long as 30 seconds or longer to load the heaviest crossbows. Because you could prepare a couple of crossbows before the other side charged, and once the other side was closing for melee, you'd drop your crossbow and draw a melee weapon.
By the time bucklers were coming around, they were designed to be used against lighter weapons (rapiers, etc.) and opponents wearing less armor. The use of a buckler was similar to the old round shields, but smaller and faster, which is necessary against something like a rapier. The point of balance is closer to the hand, which allows you to maneuver the blade more quickly, particularly the tip.
The buckler, dagger (particularly the main-gauche) or a cloak were all used to not only provide a defense against a quick weapon like that, but to hopefully push it out of position and open an opportunity for your riposte while they recover. So it has nothing to do with the speed of arming your shield. It was all about how to better defend yourself against the emerging weapons and fighting styles of the period. Note that neither were particularly useful on a battle shield with armored fighters wielding longswords and such. Neither the rapier nor the buckler were heavy enough for that type of fighting.
So yes, the inventions were designed for a purpose, but not to get around game rules. Sometimes they were designed to be faster, sometimes more powerful, etc. But on the other hand, there were a few thousand years of evolution of these types of weapons, shields and armor up through the renaissance. The designs that were developed were developed because they worked against the weapons and tactics of the time. A vambrace was designed to protect your forearm and was a fitted piece of armor. A shield strapped to your arm will rotate around your arm too much to be effective without the stabilization of using your hand to prevent it from doing so.
So like I said, it really doesn't make any difference if you wish to use it or not. Unless it makes a difference to you as to whether it's got a historical basis (not a requirement in a fantasy world), and is reasonable expected to be functional (also not a requirement). Designing and adding new types of armor, shields, etc. is just fine. But for the armor that's based off of historical types, I like to try to know how they worked and reflect that in the rules.
Regardless, my point was simply what he was describing wasn't a buckler. He asked about the origin of what he was calling a buckler. And that's it.