I personally believe you should read every vertical stretch high to low as long as you can diagnose the defense by peeking at the high before coming to the low. If you can't make the decision that fast however its best to read it low to high since you'll miss your window otherwise. As for horizontal stretches I would recommend reading them inside out. Take 4 verticals for example, you would read inside seam, inside seam, outside go, outside go, checkdown. Or you would only read half of the field and read it, inside seam, outside go, checkdown.
The most important thing is to do what is comfortable to you, find a method of going through your progressions that you feel comfortable with and build on it.
As for Switch not getting separation, you are right in one respect. The dig routes are mostly in place for zone coverages so they almost never come open versus man coverage but the post routes ran off of the Switch concept simply need pass leading to lead to big plays.