There needs to be some sort of huge reason to use both of them, stormcaller is somewhat overshadowed by voidwalkers when it comes to add control plus nova bomb has no orb cap. Sunsingers have radiance which basically define them. Strikers are basically good for pvp overall, and if you use a titan in pve, you are locked into being a defender for your team. Not to mention that they have only subpar exotics. They need a killer app or a defining role in destiny, look at nightstalkers, they came out as a huge help for the team and the other 2 subclasses are still used. Tl;dr: Stormcallers and sunbreakers need some sort of niche in destiny EDIT: i actually didnt know this post would be somewhat popular, I just thought about it, they are both reliant on their supers, just that Stormcallers have a good super.