Slack is one the most slick and pleasant pieces of software to use. It's big success as well as the fact that it's acquisition cost was one of the largest software deals ever – tells of itself – it's certainly a fine piece of software made by fine engineers who used react and electron with a certain amount of dignity. People who rant about tools like react or electron affecting their performance just don't want to understand that it's organisation and people behind the tools who are responsible for their performance.