Reached out to EA to see if I could get my key transferred over. The answer was no, of course. But it’s still annoying that I get less for having bought sooner on their platform rather than waiting for it to be available on Steam.
It most transactions, the 2 parties are the purchaser and the seller.
If you buy a game from Steam, using the steam launcher isn't a third-party launcher.
If you bought a game directly from EA, their launch isn't a third-party launcher.
If you bought the game from Steam, the EA launcher is third-party.