It is for this user.
> What would Slack gain by integrating better with my Mac?
Far better resource management, one would hope, for starters. As the article pointed out, when you're measuring your IRC client's memory use in hundreds of megs, there's a problem.
It isn't uncommon for me to need to choose which "essential" apps to turn off to get something done on a maxed-out MBP. So Slack gets turned off, and maybe someone gets annoyed that I don't respond to something, while I run a few VMs in Slack's former memory space.
As far as other things, well, using a platform's capabilities as appropriate is generally considered good form - HCI concerns, and, generally, just people like things to be consistent. I don't know why we're supposed to forget this now.
I personally don't care if Electron goes away or what, but to the extent that I'm forced to run Slack by my cow-orkers' choices, it sure would be nice if it were less of a bucket of ass.