Why is it one extreme or the other?
I defend decisions made by IDE developers because those are niche markets, but slack is not a niche market. They're "IRC for normies" (yes, yes, they fix a lot of cruft too but, it's effectively the same system).
We're not talking about hand optimised assembly, but maybe assuming that I'm going to throw 1/8th-1/3rd of my system resources into your IRC clone is not healthy.
the highest tier macbook pro can only handle 16G of memory. I had to get a special laptop (precision 5520) in order to get 32G of ram, which I feel is the only option that is future-proof for the next 3 years, and if everyone follows the slack model then it will be the minimum in less than that.