IME as an engineer who’s been around the block, before Slack we were using Hipchat, and before that Jabber or IRC. I have not noticed a significant change in features (gifs, bots, integrations were all there through all of those), just changing fads, but by god if the performance and responsiveness of the chat client de jour hasn’t been steadily declining over time.
Mostly what drove orgs I’ve been with from one to another has been pricing (Slack having a free tier ate Hipchat’s lunch, like I said), and “buzz”. Slack was the hip thing to get on in 2013.