Every single primarch had some special ability/ mutation that set him apart from his brothers Magnus was a beast of a Pysker, Valkan (spelling) was just hard too kill he got angry and smashed a land raider. Russ is said to have this howl thing going for him, Logar is learning to be a :angry: the lion is the dogs with a sword but get slapped about by Curze because he was caught out, Corax (spelling) has his stealth, Sangunius has wings can see into the future and is nails in a fight and it is explained many times in the heresy series that all the other primarchs look to him. the other Primarchs may not have a huge quirk but they have something Horus was strategist and a charismatic leader and was able to understand the strengths and weaknesses of an enermy.Dorn was totally intractable once set on his course and would never ignore and order but also knew when to fight and where to defend. Guilliman was THE strategist who held the Imperium together after the Heresy. The other Primarches do have something that sets them apart it's just a case of waiting for the Black library to get around to them if you want the Stat line crunching then Forgeworld's Heresy series will keep you happy.
So guys chill out and relax they got this.
Valkan ( tales of heresy)
Corax (ravens flight)
Sanguinius(fear to tread and other heresy books)
Russ (A thousand Sons)
Magnus (40k lore known fact)
Horus (Horus rising)
Dorn ( white dwarfs and mentions in other heresy books)