It's not hard to go back to 2.1.5. This is how I did it:
As davidfor says I went through too many steps but you can get the idea of how to do it. I love 2.1.5 compared to 2.3.[0?] although I found that PDF's worked ok for me. Still, I am reading a pdf at the moment on 2.1.5 and it is really fine -- everything is clear and easy to navigate.
You mention scrolling back to the top before changing the page -- I haven't found this to be necessary. At the bottom of the page just drag to the left. Let the screen redraw and touch the black bar. Then, in 2.1.5 after the first touch you are back at the top of the next page even though it shows the bottom of the page before the first touch.
Really, the Touch at least is fine with pdf's -- I don't know what people here are complaining about.