If the "tactics" are not something that a player can be realistically expected to work out over the board, then, is it necessarily a mistake to try an opening book?
Now you're trying to coerce me into saying that reading an opening book is a mistake?
To avoid this meandering back-and-forth argument that you seem intent on dragging on, I'll make my position clear: if you want to improve your opening play, work on your tactics.
This is my opinion on the matter, and no amount of rhetoric or leading questions will get me to change it.
You're welcome to disagree all you like, and I'd expect you to do as much. There's no universal law that says all chess players must agree.
I would say, though, that there's certainly one approach that won't help a player improve their opening play: by spending too much time arguing on a forum about opening study. Use that time, instead, to work on your game.
This applies to me, as well—so with that, I bid you adieu.
I can say that I agree with your quotes by Giddins and Nunn. That's kinda how I try to approach the topic, though I think that I have a lot of basics to cover before I should dive in into openings much further than I have so far.
As far as Yusupov is concerned, I won't disagree with him in general. This said, I own the first book of the Yusupov series and had to put it on the shelf again, because I don't think that my level of play is where it would need to be to get most out of the book. As far as I have learned in the meantime, general consensus is that those books actually are a bit too difficult compared to what they announce on the (german) title. And from what I gathered from other sources, it seems that German DWZ 1500 equals ELO 1700 in average.
But, relating to this topic, from the 24 chapters of the first book, only two handle opening related topics (basic principles in chapter 4, gambits in chapter 24, the rest is mostly tactics and a bit of strategy). So it doesn't seem as if Yusupov's idea of how to train players much stronger than me would be to teach them the study of openings first and foremost.