Interesting viewpoint, and I get where you're going with it, but honestly, some of those phrases are actually phrases that I use sometime, in my style of writing. Word's like "let's" and "we'll" are good ways to make the reader part of the story, and "so" really is such a casual comment, that I find myself using it for easy conversation flow. But I do truly see what you're saying about the sudden change in tone of the writing. Sometimes, it's so blatantly obvious, it's funny. Thanks for sharing your thoughts :-)