>>538082480
Primaris™ still can change equipment, still are trained in a variety of weapons and start as Scouts. In campaign last mission Titus considers deploying in Gravis™ armor. And during one of the earlier ones in idle talk one Marine reminds another to take a flamethrower with him. Intercessor™ Marine can take plasma and join Hellblaster™ Squad or Infernus™ Squad or any other as needed. This is why we have "Tactical" as a class here instead of all those Aspect Warriors. Marine could start combat as an Aggressor™ in Gravis™ and then as his armor take damage he could strip into Tacticus™ configuration and then into Phobos™.

Lore issues are nonissues at all. All that is really needed is a character selection tab above classes. So you can simply choose if you want to play as Straban or Decimus and then separately select a class. Low effort solution would simply disable some voice lines. Higher effort one would make few separate banter options. Like teammates bullying Deciums if he is forced to be an Eliminator™ while he seethes about being forced to be far away from melee.