The native client they were referring to was mIRC, which does much less than Slack does. A better comparison might be Discord, which performs much better than Slack and is also written in Electron. VSCode, written in Electron, performs much better for me than Visual Studio (a native app), but I wouldn't use that as proof that Electron is faster than native apps because Visual Studio does so much more
The major differences I can think of off the top of my head are threading, reactions, voice chat, and history. Voice chat is the only one that should use significantly more resources than mIRC.
