You are also forgetting the psychological impact that a few seconds can make. After 3 seconds of waiting without any progress indicator you've general

You are also forgetting the psychological impact that a few seconds can make. After 3 seconds of waiting without any progress indicator you've generally lost the attention of the user and they will do something else in the meantime. When your talking about spinning up a MASSIVE number compute threads/servers >128 instances. This also takes a non-trivial time. You really aren't seeing the forest though the trees. What I'm saying is it is a trade off. Time gain: 1/2^x Resource spending: 2^x Figure out where the intercept based on cost.