It's like retailers said. GamesMaya said that actually, PS4 hardware sales increased when Tales of Berseria launched. However, retailers reported stock problems during the weekend. As a result, PS4 stayed flat this week even with the release of ToB, due to weekend shortages.
Next week, the drop will be big, with a full week of shortages tracked. (And also the Slim leak announcement).
Media Create Annual Archive (Spanish version)