Alerts that monitor other alerts

Sure, you can use Service Insight for this, but it is a premium feature, which is using an expensive mallet to handle something that should be available without that extra cost.  Or, there should be a Service Insight light for this stuff, leaving the costly part for the intended enhanced features of Service Insight (like Kubernetes).

My recommendation on this was to extend cluster alerts so you could at least match up instances.  My use case at the time was to detect an AP offline on a controller cluster.  There is no way to do this without SI, which as you say is complex, and it is an extra cost.  We need stuff like this in the base product.