Quote Originally Posted by Daemonette666 View Post
If I were to team up the Primarchs to be either counters or similar/akin type Primarchs I would list them as follows.

Angron - Russ (both frenzied fighters who rush the enemy head on preferring close quarter fighting)

Vulcan - Ferris Manus ( both weapon smiths who have dealing with the mechanicus, though one more than the other)

Conrad Curze - Sanguinius (both use rapid strike forces to take the enemy by surprise dropping into the heart of their defences and have a greater ammount of jump troops in their forces)

Lion El 'Johnson - Guilliman (knightly warriors who use tactics and combined arms forces to their best uses)

Perturabo - Dorn (Seige and defence specialists)

Fulgrim - ?

Jaghatai Kharn - ?

Alpharius - Corax (both use stealth and sneak tactics)

Lorgar - Magnus the red ( Both seek knowledge, one through sorcery, the other in search of faith, a purpose , a god to worship)

That just leaves Fulgrim and Jaghatai Khan. Both are as un related to each other as Angron is to Magnus. I would propose that the missing Primarchs are their counters. One who tries to achieve perfection in everything, the other who strives to live on the move, always trying to find what is over the next hill, the next experience, hence his use of bikes, rapidly deployed troops in fast rhinos, lots of jet bikes (in the early days).
I would pair Sanguinius with Fulgrim (both pretty boys who love art and culture as much as, if not more so than warfare), and Cruze and Corax together (in Deliverance Lost, Corax explicitly muses on just how very similar he and Cruze were, and how easily the two might have had their roles reversed but for luck and chance).

You also left Horus and Mortorian out, and the matching of Lorgar with Magnus seems forced.

I feel that it would be likely, given what the Emperor ultimately planned, that there would have been another Primarch with vast psychic potential in addition to Magnus, as otherwise that was the Emperor putting all his retirement eggs in one basket with Magnus.

I would have also paired Guilliman with Horus, as both were more than just warlords and generals and potential heirs to the throne.

I think those are the easy pairings, the ones left do not easily match with any of the others.