You can of course, but how about these?

(function(){ var a=function(){};a.prototype.toString=navigator.credentials.create.toString.bind(navigator.credentials.create); return new a();})().toString == Function.prototype.toString

yields false where

navigator.credentials.create.toString == Function.prototype.toString

yields true

Of course you can "just" modify Function.prototype.toString as well. And so on.

You know what that can be detected as-well. I'm trying to prove my point that it's endless cat and mouse game.

I think we're talking past each other then.