I made the jump from SystemMonitor2 to ArcGIS Monitor 10.6 and miss the ability to have a "Reports" page with a few graphs of the metrics I look at most frequently. I would usually leave it open in a tab and could at a glance see how several metrics were behaving over the course of the day/week/etc. and look at individual collectors more deeply on their own pages if something looked odd but hadn't triggered an alert yet.