I am insanely confused by this comment. So it slows down deboarding for some people to be already standing with their things ready to move forward, and speeds things up for literally everyone to first have to stand and then get their things? Seems like a fraction of the plane being ready when the doors open would inevitably speed things up a little. Sidenote: the real dickheads imo are the ones who get up and then move up to the front of the plane. They are effectively skipping line to get off and it's such a dick move. I want to strangle people who do that.
But back to the post, what OP and I seem to notice is just how damned slow people are. If I have a window seat and a bag overhead, it still probably takes me under 15 seconds to go from seated to having my bag and moving. I watch people toward the front take FOREVER to do the same thing. Then they have a bunch of kids and that magnifies the issue even more.