Cannot use my own polyfill for React Native Object.assign - reactjs

Question

Due to this issue https://github.com/facebook/metro/commit/9773229227895bfc5a5bde969108a4cbcc270eab#diff-ce1179d24387784c3c5f856c4b5b55d8R59
Object.assign fails on dev builds for RN under certain scenarios (which is explained in the above link's comments). The issue is that one of my node modules triggers this particular scenario. I need to polyfill for that reason.
I'm trying to polyfill my own Object.assign (based on this https://github.com/facebook/react-native/blob/1151c096dab17e5d9a6ac05b61aacecd4305f3db/Libraries/polyfills/Object.es6.js, except without the check for an existing one)
When I log out global from within the node module, I can see that it is pointing to my code
Object: ƒ Object()
arguments: (...)
assign: ƒ assign(target, varArgs)
arguments: (...)
caller: (...)
length: 2
name: "assign"
prototype: {constructor: ƒ}
__proto__: ƒ ()
[[FunctionLocation]]: objectAssign-polyfill.js:2
[[Scopes]]: Scopes[1]
However, the node module still appears to be using its own Object.assign rather than my polyfilled one.
When I modify the code in the node module to use global.Object.assign, it seems to finally work. However, is there a way to do this without doing that (because then I'd have to do it everywhere)?
The code is below:
// objectAssign-polyfill.js
Object.defineProperty(Object, 'assign', {
value: function assign(target, varArgs) {
'use strict';
if (target == null) {
throw new TypeError('Cannot convert undefined or null to object');
}
let to = Object(target);
for (let index = 1; index < arguments.length; index++) {
let nextSource = arguments[index];
if (nextSource != null) {
for (let nextKey in nextSource) {
if (Object.prototype.hasOwnProperty.call(nextSource, nextKey)) {
to[nextKey] = nextSource[nextKey];
}
}
}
}
return to;
},
writable: true,
configurable: true,
});
// shims.js
import "node-libs-react-native/globals";
import './objectAssign-polyfill'
import { btoa } from "Base64";
import nodeUrl from 'url';
global.btoa = btoa;
global.URL = class URL {
constructor(url) {
return nodeUrl.parse(url)
}
}
// index.js (the root of my RN app)
/** #format */
import "./shims";
import { AppRegistry } from "react-native";
import Core from "./Core";
import { name as appName } from "./app.json";
AppRegistry.registerComponent(appName, () => Core);