Schwarber has to be counted in the top 3 or 4, but I agree with your point. They all need to start doing better.
I've never been one to think a player's last 5, 10 or 20 game sample size is a good predictor of what will come next, so I fully expect all of these guys to pull their weight going forward.
There is no reason to think otherwise.
Of course, players slump, all the time. One of these guys may not do well, but my guess is that 3 of the 4 do wonders, and by that I just mean do what they normally do (.850+).