Agreed David - there are several things I try to think about before I comment on an image here (and elsewhere).
The first is the abilities of the poster. This is related to his or her current level as a photographer, whether behind the camera or in post processing. The response needs to address issues at a level that is useful to the photographer.
The second is context - suggestions on improving a snapshot image that is destined for social media will be completely different than one that is a fine art project that will end up as being a print hanging on a wall. That is the one thing we sometimes tend to forget about when commenting on work.
The third is the pedagogical impact. Members and outsiders look at work and comments to supplement their own learning, so the audience is often far broader that the simple conversation between the poster and the respondent.
As for processing an image in minutes. That's all about developing a workflow that works for you and refining it so that you can execute quickly with consistent quality. It's also about working on images that only require a few minutes of edits. I have started preparing five B&W images for a print competition that will be running next May. I expect I will spend around 2 weeks working on them simply because that is the level of effort required to do well. It's all about the context...