I know you don’t, and that is fair :-)
So, here’s the more detailed version of my response:

The first 7 paragraphs are basically you asking a lot of questions and then you go about half-answering them; half because you ask if UX Strategy is “real” while linking to very real books, articles, and events, and half because you mix statements of what other professionals do (“Not all strategists are made the same”, “Both lenses are actually remarkably similar”) with your own answers (“I see strategy as…” and “I think a lot of it comes down to…”). So I am left wondering: it this an opinion piece, advice for UX practitioners, or a call for clarity in the industry?

Then you continue with “I’m not sure if anybody has taken the time to really define what product strategy is”. Well, several people have, and it’s pretty well-documented, for example here: https://en.wikipedia.org/wiki/Product_strategy#References
More generic definitions of Strategic Thinking https://en.wikipedia.org/wiki/Strategic_thinking and Strategic Planning https://en.wikipedia.org/wiki/Strategic_planning are helpful too.

Your own definition of product strategy is “using the processes and practices of the internet age to help deliver successful digital products”. Why do you include “of the internet age” there? Have processes and practices from before the internet age not worked to define product strategies in the past? And what is different about digital products that requires the use of new processes and practices?

Then you confuse my in this sentence: “I think UX strategy is similar to product strategy, in the same way that business strategy is similar to marketing strategy”. I think you wanted to switch one set of strategies around, since it’s “<deep> is similar to <shallow>” in the first half, and “<shallow> is similar to <deep>” in the second half. Right?

Next, you state “UX strategy tends to look at a digital product or service through a user-centred lens; how will a user experience the product, and how can we make that experience as positive as possible?” and in the next paragraph something similar: “User Experience strategy draws on the practices of user experience design to help describe what the experience of the product or service should feel like.”
In both cases I think you’re wrong because you describe things that UX researchers, designers and evaluators already do; they don’t need a strategist to do that with/for them.

Finally, and as indicated in the earlier comment, you make sense where you write “UX strategists will explore possible new product or service scenarios, advising senior management which direction they should take. Once a decision has been made, they will help communicate the target experience to the wider organisation through concept models, diagrams and other abstractions. They will then oversee the delivery of that vision, to ensure the final output meets the stated goals.”

From talking with fellow UX Strategists, by attending UX Strategy events, by reading a large set of related articles and books, and after fulfilling the role of UX Strategist at a couple of employers in recent years (see e.g. http://www.slideshare.net/pboersma/sdl-added-strategists-to-a-ux-team-ux-strat), that is what I have learned is what UX Strategists do.

So, yes, UX strategy is a very real thing but — in my experience — different from how you describe it in your article.