Any suggestions? I've a top of the line macbook and the two things it has the hardest time handling are Chrome and Slack... I think Chrome needs to start thinking more about performance and design.

You can use now Slack to XMPP or IRC gateway and use native client for these protocols - as a result power consuption is greatly reduced. A minor problem is that Slack has no idea if you read the message or not (though they should easily fix this with XMPP gateway).

#no-to-calling-electron-a-native-app-movement

I recently switched back to using Slack in a pinned tab and I can't recommend it enough. The minor additional inconvenience of getting to it makes it less distracting for me