Looks like the main features are arguably better defaults, libcaca support (basically useless anyways), and profile support (how often do you really need to check someone's info that you don't already have stored in the app).
didn't they deprecate the gateway last year?
Wee-slack is a gateway for weechat; it uses the slack api. But weechat can function as its own proxy (client/server split between the gui/tui and the network bits).