The problem isn't that scrappers can't differentiate between stalkers, it's scrappers can't differentiate from brutes. Who are a much better comprised between tank/dps with a taunt aura so that AOEs are also more effective. Scrappers need their own unique role to continue being a popular class. I think like stalkers then need skill changes to their power sets instead of just different %. Honestly I think giving offensive secondaries (like shields) to brutes was a huge mistake, since it made scrappers a lot less unique.