I suppose the answer to the question about focus is habit. It's been a lot of years I've done things that way, and it's in muscle memory to highlight that way. So it's disorienting that it's gone. Don't even have to move my hands out of home row to do it.
You're right about the comment boxes. I just ignore them. The main thing is, efficient highlighting for the documents I'm working on. I don't need to export, don't need to do anything but draw my eye back to text I care about.
As you say, this is sand-in-the-head thinking, as highlighting while reading is a pretty common practice. In Word you can do it with one click (not sure if they have a keyboard equivalent, as I use Word as infrequently as possible, and have never investigated). Pages '09 was fine that way! But navigating through two or three levels of mouse clicks to make it happen is not on. The function key shortcut helps, but as you say, then that has to be built into a cross-document template. That's something the app should handle itself, and up until a couple of days ago, it did, at least sufficient for my purposes. Now broken, and I have no idea why. I do however appreciate the workaround suggestion. Still would prefer a fix, however.