It's not like you're stuck with ugly terminal only clients anymore. There is KiwiIRC, IRCCloud, and several other great web clients that not only let you connect to any server but provide bouncer services and backlog. There are also plenty of easy to use native clients that don't require any configuration.
There are some benefits of Slack, but the ones you mention aren't them. In fact, seeing how you CANT host your own Slack server I would say "difficult to host" is a flat lie against IRC.