As I was reading through this, I think the general misunderstanding I was seeing (that maybe you've recognized now) is that Ignition Edge isn't required if all you need is a client on the plant floor. If you're going to have a central gateway running on something more powerful besides an iPC hopefully, you'll only install the client software on the local HMI computer (which works great for iPCs) that connects to the central gateway.
Edge is useful for cases where you're having remote sites or stations that are physically distant from the main network that need to run independently of the central gateway. It works well for standalone skids as a PanelView replacement. Where the skid is autonomous from other systems, and even then, if it's on the same network as the central gateway, you could (if you want) run the HMI normally off of the central gateway, but fail over to the local client in the event of a network break.
As Phil mentioned, if you're looking for a replacement for a PanelView, stick with Vision. Even on larger plants, I try to stick with Vision for HMI control of the plants, but when doing a SCADA system to monitor lots of plants and not primarily doing control from the system, Perspective works well for this. Use the right tool for the job. I've only once put Perspective on a local PanelView replacement where the customer wanted access to it from his phone on the local WiFi router in the panel and this was a standalone skid.