That's not quite it. The issue is that there's no other traffic bound to that IP - ECH doesn't buy you any security, because an observer doesn't even need to look at the content of the traffic to know where it's headed.
Maybe it will be more useful for outbound from NGinx or HAProxy to the origin server using ECH so the destination ISP has no idea what sites are on the origin assuming that traffic is not passing over a VPN already.
Maybe it will be more useful for outbound from NGinx or HAProxy to the origin server using ECH so the destination ISP has no idea what sites are on the origin assuming that traffic is not passing over a VPN already.