Get off Aski.

I've been using Discord for quite a while, alongside ICQ, and haven't noticed any drawbacks. Regarding the usefulness of message history: I often needed to access chat logs with players, sometimes going back more than a year (both for in-game and judging purposes). In QIP, they were simply stored on the computer as text files and couldn't be lost. If Slack has problems with this, then Discord seems like a better option.