As a developer, (with a lot of js experience) I sympathize with devs trying to build a product that works seamlessly crossplatform. Electron is a great value when you want to push out a product fast that serves a lot of users accross all devices and you have limited resources.
But I'm calling out slack specifically. you have millions in funding and profit. You can afford to hire a few more devs to make a polished native platform optimized version for each platform that is resource efficient. Slack runs on my desktop all day so having it run fast and not take up too many resources would be a huge win.