We’re also trying to run Headless, on a Shipping Build, which improves performance by a lot and we know only by using a Custom Unreal Engine version will have a chance to do so.
But what exactly have you disabled, that gave performance back, that would be good to know really.
From our perspective, we’re trying to Disable Components (WidgetComponent etc.) that are not needed in Headless mode, but still running with each Client.