cockpit dependency

That's probably more helpfully phrased as what can Performance Co-Pilot do that Prometheus/Grafana cannot. To my first look it didn't seem if pcp added any value if you already had Prometheus configured or needed something outside its ecosystem, but if you were starting from scratch and wanted to stay within the ecosystem of built-in tools (such as Cockpit) you could invest in pcp with central collection instead and get pretty much the same performance metrics as Prometheus..