I definitely agree that Line is much easier to use.
The thing with Discord chat rooms is that they’re only as good as the moderators who organize and manage them. It does really require some time out of their day to keep the rooms neat and tidy, which is understandably a turn off for users who just want a quick chatting app with their alliance or a group of players.
The worst discord rooms I’ve been in are the ones that lack such organization, where the @everyone tag is spammed in particular (omg that becomes a bother).
The good Discord rooms, however, are very easy to follow and engage in conversations. It works well for me, as I use it for other game communities, and I can jump between the channels depending on the game I’m playing. 