Absolutely, you're probably right if you meant to imply that the percentage of such users is low. But on the other hand, if Slack became as fast as desktop apps from the 1990s tomorrow, how many users do you think would raise their arms in joy and exclaim that their computers suddenly became much faster? Latency is less directly visible to users - which is probably why it receives less attention - but silently adds to the users frustrations when working with the system.