I've been looking for an answer to this thread since I bought my Galaxy S9 and Samsung introduced the Aremojis. It was fun creating them and Samsung put the one or other update to make them more appealing, but never really used them in chats cause they are being sent as Gifs and get saved in my contacts' Phone storage. You will end up deleting them if someone uses them a lot and sends you the same expressions over and over again. One UI 2.1 did not change that.
I'm not sure if the younger generation uses it, but as you said, I feel that the whatsapp stickers are more liked because they just get saved in the chat history and will send as soon as you click on them.
Curious what Samsung's answer would be on that.