Yes, I think the Scythians are likely the origin of almost all of the Asiatic and European cultures, the Chinese and Egyptians being the only exception (though they had substantial direct influence on the Chinese).

I think the reason the Scythian Empire lasted so long was because of ease of movement. They were "horse lords," though not exclusively (they also had numerous cities). They created all the "ancient" roads (Silk Road, Amber Road, etc.). Beyond the roads however, they were based primarily on the Asiatic Steppes, which provided a natural path, with amazing mobility all across Asia and Eastern Europe for their horses and wagons and "gypsy" style mobile homes (they were also the origin of the gypsies). This natural highly mobile path was perfect for trade and control of such a large Empire with their unmatched, elite mobile horse troops (more recently called the Cossacks).

There were natural boundaries however (mountain ranges, seas, etc.) and along those boundaries, exchanges (trade, culture, genetic mixing, tribute) between the outposts and Central Authority was reduced. So while they may have been the seed of all those far flung civilizations, the ones that were too far away from that central path (the Steppes) tended to be less likely under their direct control as time went on. "Direct control" means Tributaries AKA Principalities that paid Tribute to the Central Authority and were "on call" for any war effort some Khan of Khans decided to embark on (there were many more than just Attila and Ghengis).

Events like Attila the Hun, or Ghengis Khan were reconquests of these principalities that fell away, not conquests. The Goths, the Gauls, the Scots, the Irish, the Welsh, the Vikings, the Moscovites, the Slavs, the Greeks, the Macedonians, the Romans, the Iranians, the Arabs, the Indians (in India) etc. were all Scythian outposts. The ones furthest away from the Steppes spent the least time under control of the Central Authority. So, for example, the Scots were pretty far removed from the Scythian roots, and thus just a Scythian seed, where as the Moscovians, being very near the Steppes were almost always under direct control, until they declared independence and began breaking away in the 16th century.

I've written over a hundred pages on the Tartarians/Scythians. At some point I will finish it and publish it.