The Slack dev you're quoting doesn't mention any of your points. His points were that the native extension API was clunky (DeskGap could improve upon this), that users of old OS versions are completely left out in the cold for updates (he mentions severe UI bugs, which is very different from "we need bleeding-edge Chrome features"), and that the difference would be negligible anyway since the poor RAM and CPU usage is from their own garbage JavaScript code anyway, not the browser engine.