Other than the Mongols (and arguably with the Huns, whose reputation as pure evil is IMO mostly unwarranted) none of those groups are remembered for destroying cities or murdering thousands of people. Magyars come closest, but considering that they shared Europe with the vikings their brutality was far from exceptional. Scythians and Cumans have more of a "noble savage" reputation if anything.Huns, Scythians, Avars, Bolgars, Magyars, Turkomens, Mongols and Cumans just to name a few steppe nomads who left an enduring reputation for brutality and rapaciousness.
Are you referring to your last EUIV game?
EUIV portrays nomads as city-flattening lunatics. The sacking mechanic is ridiculous. Nomadic empires were normal states populated by normal people who didn't have some savage drive to murder and rape for no reason. The Mongols were the only nomadic empire that killed millions of people, and even that was just an extension of the ordinary medieval approach to warfare.