So Ripcord is created by one person in his spare time and it performs blazingly-fast and supports Slack whilst Slack's own client is maintained by tens if not hundreds of engineers and it still performs slower when joining more teams, consumes significant amounts of RAM and they create this blog-post about performance improvements whilst still using Electron.
Understanding on why Slack is unable to create a performant desktop-client for their users is beyond me. I also wasn't able to use Slack and Discord at the same time on my MacBook without it swapping on the SSD. So Ripcord seems to be a good lightweight alternative for me.
I just wish it supported Keybase Chat so I can ditch that Electron garbage too.