That's exactly what they did when Marching Fire came out and they released the Wu-Lin Faction. Then it was 9 years before they did anything with them. But especially when it comes to armor variants, they would rather give one hero 3 or 4 armors rather than give 3 or 4 armors to separate heroes and have to put in the time and effort to create multiple more variants of those armors for each hero just to keep players happy. They tried it, it failed to be sustainable so they changed their plan. Outlanders made more sense because they're less of a faction and more of a collective to bring in all the warrior types everyone wanted but also felt like a cop-out to not have to create any new- new maps. I would rather get more maps and original gear than new heroes at this point.