How can I disable Server.app's Webserver?

I've installed Server.app on a new server I'm configuring. I'm using Server.app for VPN, Mail server and some other small stuff. But I'm not using the built in webserver. I need a lot more than Server.app has to offer.

THE PROBLEM IS, even when you have the web service turned off entirely, it's still running. If I visit http://localhost, i get a generic placeholder page. This prevents my homebrew installed apache from running, because of course they fight over port 80. So I need a way to kill it. JUST AS IMPORTANT, It needs to stay killed. I can't have a software update replace a .plist somewhere and suddenly have this default web server turn itself back on and knock my real web server offline again.

I'm upgrading from an older Snow Leopard server and I am disgusted by my experience with Server.app so far. I've used it casually for things like netboot serving over the years, but this is my first attempt at setting up a real server with it.