I'd agree that there are some things you want always visible. But I'll also argue there is a benefit with having engine data connected to the main chart plotter, and it's ability to display it. On the Raymarine (and others, I imagine), if there is an engine alarm, you will get a large pop up window on the display and an audible alarm. That will happen even if no engine data is displayed normally. This will get your attention critical seconds or even minutes between scanning the engine instruments.
In addition, the newer chart plotters have some nice engine related features. For example, the RM Axiom (and again probably others) will keep track of fuel useage instantaneously, by the day, week, month, and season. It won't do that unless engine connected.
All these assume an electronically controlled engine.
I'll put in a plug for Raymarine: in the C80 days, they were having trouble as a company in innovation, service, and quality. Since the Flir buyout, it's become a different company. They seem to be a bit ahead of the others in innovation, and accelerating. Their support has gotten much better, frequent software updates adding features long after purchase. And the prices are dropping.