Fatebringer and vision of confluence were used extensively because they are great weapons, yes. I say the solution is to create other weapons on par with these, guns that are actually fun to use like these two. Given the track record of the weapons they added in the previous two dlc expansions, are you really confident they can deliver other fun, worthwhile weapons on the same level?
Rather than saying, "You're having too much fun with fatebringer, we want you to use something else. It's now obsolete, use these new weapons." The sentiment should be, "Fatebringer is a fun and incredibly useful weapon, here are some more that compliment that experience."
TL;DR
They need to make us want to use other guns by making them fun and effective, not force us to my making the fun guns ineffective.