Yes, you can buy the "packs" from anywhere they are sold, and you will be registering them on Origin. They all sell you the keys, then you have to put the keys into Origin to play.
It used to be that you could choose disks or another platform that offered them, but since at least 2014 Origin has been required no matter what. Maybe it cuts down on theft? It certainly cuts down on resales of used games because you don't have disks to resell.
My son, who only buys games on Steam, complains about it on a near daily basis. He only has one game that is EA, but it forced him to have both clients on his computer.