High impact fusions (wizened rebuke and Erentil) should not be able to roll backup plan. Regardless of their lethal range (Let's be honest, it's way too much.), part of countering fusions, especially of that archetype, is sound queues. You hear it charge, so you bait the shot and then punish. Simple up close, annoying when you get mapped at a distance you should have been safe. Also, the disadvantage of high impact fusions is their charge time. It's the longest in their class, as it should be. Backup plans eliminates both of these. Sound queues go out the window. Charge time becomes nonexistent. And the lethal range doesn't change very much at all. Certainly not enough to warrant the advantages of the perk. So in short, high impact fusions should not be able to roll with back plan, as the perk currently eliminates the key disadvantages of the gun with no drawback and eliminates a key aspect in countering the use of fusions, i.e. sound queues.
As an avid Fusion Rifle user, they need to be toned way the hell down. A charge time does not dismiss the fact you can still pre fire it. With double scavenger perks you can literally run around the map lasering people from scout rifle ranges. To be clear, this could not be done in D1.