That's why I use Discord, the free tier has _unlimited_ history. The client itself is lightweight, and it's an incremental improvement on IRC in many other areas, as you would expect. Still using IRC of course :)
There's a lot to like in Discord, and it rapidly became the go to client for all my gaming related friends and activities, but it suffers from the same root pitfalls that Slack always has. It will inevitably run out of VC money (or whatever they're spending now) at some point and start wanting to actually turn a profit.
I sure do hope this is sarcasm. Surely you do know this can go away at any time.
The problem with better chat is that it's better, so you spend more time on it.