We look at most of the tools, many of the buildings and materials used in the show and hey seem to reflect ours: being made of iron and steel.
So it's not too much of a leap that Equestrian progression of metallurgy mirrored ours as well. Which means ponies also followed our downgrade from bronze to iron.
Contrary to popular belief, bronze is actually a superior metal to pure iron, being harder, far more corrosion resistant and easier to craft. It could even be on par with mild steel. This was the go to metal of the ancient world.
But then the bronze age collapse happened when the rare materials needed to craft bronze began to dry up, among other things. So people switched to iron. An inferior metal that was prone to rusting, prone to bending and harder to work with. But it was far, far more common, and thus easier to craft locally with out the need of transcontinental trade networks.
In Equestria, along with the inconsistencies in technology, we see inconsistencies in the metals used. For the sky scrapers of Manehatten, railroads crossing the continent to many of the tools the characters use, we see iron and steel. Yet in much of Canterlot, we see gold like spires, roofs and accents. Doubtful it's all actual gold, cause gold sucks as a building material, so it's most likely bronze. Same with the armor of the royal guard. Doubtful they'd go through the effort of painting all that gold either. Seems very un-regal. Yet those same guards appear to have steel spears.
So what is with this odd mix of metals? If iron is so accessible, why go through the effort to use so much bronze? And if bronze is still available, why make the switch to inferior iron?
Is Equestria in an iron age or a bronze age?