@FPSKiryu
Correct, those cosmetics would still be on the original EA account. If you moved your Xbox account back you'd be able to access them, but there would not be a way to transfer that to a new EA account unfortunately.
It may help to visualize it this way, you've essentially turned this:
Old EA account: Xbox account, Xbox progress
New EA account: Steam account, Steam progress
...into this:
Old EA account: Xbox progress
New EA account: Steam account, Steam progress, Xbox account
So, you could re-link the Xbox account to the old EA account and move the Steam account there as well, though you'd lose access to your Steam progress in that case. If you'd prefer to keep the Xbox content instead however, that may be an option to consider.
If you're unable to set up a link directly, you can reach out to support so they can assist further. If you create a new case here and select Game Support > The EA app > I want to update my EA Account information, you should be able to get in touch with the support team so they can take a look if needed.