It would seem that all Linear Fusion Rifles also received the damage reduction against Champions that was intended for Arbalest.
Someone else has done all the work for me, so I have just included a link to the reddit thread that has videos and other damage tests.
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That makes alot of sense cause I just ran the nightfall and was shocked how little damage I was doing with Stormchaser to champs when Stormchaser was doing so much more to bosses. But you do have to remember that you do less damage with all guns to champs until they are stunned and when they are stunned you do way more damage. But I was only doing 4k for body shot with Storm but with Vex Mythoclast was doing 800 a body shot when it fired ssssoooo much faster and wasn't heavy. I ended up stopping using heavy on champs and just used my Vex. It was too hard to land precision shots with Stormchaser while they were moving anyways.