Basically...I'd say this has more to do with the fact that Slack's development team doesn't get enough control over their applications in order to make things like this happen faster.
What I mean is: perhaps the path of least resistance (and thus the cheaper way) does not lead to good performance by default.
If only platforms and frameworks would make the fast way easy, and the slow way hard, it would be simpler to have faster software (not that it's easy to do).
Now, if only all programs had performance tests on all commits (like browsers use speedometer 3, and track the trend over time, because they know it matters to users).
- Syntax Colorization of large source files.
- Auto-Completion Performance
- Rendering on Navigation when line lengths are very long.
Only thing Vim/NVim faster is Start-Up speed.
If someone care about speed actually, try Kate and Zed
A bloaty runtime (primarily because it's not shared across processes, as every app brings its own private copy of Electron) enables running the horrors of modern web development, i.e. pulling in thousands of libraries, sometimes each in several versions.