It's possible the SPOD isn't being caused by the suspected app, but by another app or daemon that may be running in the background. You can usually tell if a specific app, such as Safari, is causing the slowdown by bringing another app to the foreground. If the spinning pinwheel or beachball cursor goes away but returns when you bring the Safari app back to the front, then it's likely Safari that is having an issue. But if the SPOD continues when you switch to another app, then another app is causing the problem.
I just finished updating my Mac to 10.11.5 (was at 10.11.4). My machine was already running the latest Outlook 2016 patch (15.22). After testing, I found that Outlook 2016 was slow at first, with the spinning beach ball, when: - starting up - switching from Mail to Calendar the first time for a given session.