It is true that early metallurgy (copper, gold, silver) developed first in the Balkans and central Anatolia, most probably with G2a, J2 and E1b1b people. But from the Bronze Age R1a and R1b people became the leaders in metal working technologies. What is particularly amazing among steppe people is not that they developed bronze working early (there is now
evidence that the first bronzes might have been made in the Balkans too), but that most of the population seems to have been involved one way or another in bronze working. The so-called 'country of towns' of the Sintashta culture contrasted sharply with contemporaneous West Asian and South Asian civilizations in that every single house showed signs of bronze working. For the early Indo-Europeans metallurgy wasn't the work of a small specialised guild, but a way of life in itself.
Another difference is that steppe people had a far more militaristic use of bronze that Near Eastern societies. The contrast is striking when we compare bronze objects from the Maykop culture, in the Northwest Caucasus, with those of the contemporaneous Kura-Araxes culture, in the South Caucasus and eastern Anatolia. While most Kura-Araxes bronzes were functional (e.g. agricultural) and luxury objects, those from Maykop are overwhelmingly weapons (including the world's earliest swords).
The extreme militarism of steppe Indo-Europeans certainly explains how they managed to conquer such vast territories so quickly, and defeated civilizations that were seemingly more advanced in many other respects.