Hey @PhantomSquat,
Just to add on to what's been mentioned here, we do have a breakdown of how various games interact with Origin/Steam here: https://help.ea.com/en-us/help/pc/troubleshooting-ea-games-on-steam/
Notably in this case:
If I have already purchased a game on Origin, can I play it on Steam?
No — games purchased on Origin can only be played on Origin.
While you can manually add non-Steam games to your Steam library and they'll technically appear there, it will still launch Origin to start the game if it was purchased on Origin.
If you purchase this title on Steam you will still need to connect it to an Origin account as part of the install/launch process.
Do I always need Origin to play EA games in my Steam library?
You may need Origin to launch some EA games from Steam.
When you do, Steam will tell you the game needs to be launched using a third-party DRM and will show Origin software installation in the system requirements.
In this case the game may appear in your Origin library, but will still open Steam if you try to install or launch it from your Origin library.
Essentially Origin will be used to some extent in either case, but you should ultimately expect to be using the launcher for whichever platform the game's purchased on.