It's easier than making the UI and server faster for sure, I'm just not sure why engineers don't insist of fixing things the right way.
Einstein figured out why in 1907, and most of us have just been going along with the assumption that superluminal communication just isn't possible.
In majority of cases, I assume network latency will be the dominant factor, and that is outside the control of the engineers.
I happen to use slack from hardwired gigabit ethernet to a gigabit fiber internet connection. But I maintain some awareness that some others may use it from their older android phone with 2 bars of service, or on a laptop with 27 open blasting wifi spots, etc etc etc.
I will therefore put forward that assumption you can ensure instant communication, is the wrong wrong wrong way for engineers to write code...
That's like saying "just fix global warming", it's more complicated than that.