If memory serves, being forced to sign into Slack for all eternity is one of the circles of Hell in Dante's Inferno. Even if that's a completely fabricated statement (which it is), it drives home the point of how annoying Slack sign-ins can be. Now, it's slightly less terrible on Android thanks to Smart Lock support.
Previously, Slack would just ask you to enter your room ID, followed by your credentials. Remembering multiple Slack room names in addition to the logins can get annoying, and the Slack "Magic Link" method never worked very well. Smart Lock is an optional way for developers to automate sign-ins using the passwords you've saved in Google. In the new beta, all you need to do is select the Google account associated with your Slack rooms. If you've saved your password, Slack will sign you in.
This feature is only live in the beta version of the app so far, but you can join the beta instantly via the Play Store. I ran through the Smart Lock sign-in with the beta app, and it was much less painful, even with Slack chats under several different Google accounts. Remember, you'll still need to enter two-factor codes manually for any rooms that require them.