I think we have a philosophical disagreement there. I don't get any added sense of achievement by sitting through a few scripted sequences, pressing alt-N a couple times, and then pressing 1 (no matter how great the presentation was the first time). I already know I can do those things, so there's no achievement in doing them again.
I get a sense of achievement from actually overcoming the hard part (the combat), and when I fail at it I want to get right back to it. Knowing that I need to sit through a bunch of easy but time-consuming mission to get back to the hard part discourages me from trying.
In a sense, once you've done it once, all the mission 4 content before the Guardian battle is just a load screen. I think you can agree nobody enjoys a five minute load screen.