In the middle ages, someone might have posted a similar question: "Are military strategy books like Vegetius and the Aeneid useful?" And the answer would have been a resounding TL;DR yes.

But not because a Roman military theorist or a Roman poet imagining the Greek mythic past really had much to do with medieval warfare. The events in the Aeneid never happened, and the military system of Vegetius and the Roman society that supported it were both parts of the distant past, long before Charlemagne rose to power.

Instead, these texts offered a language for discussing war and a ready vocabulary that could be adapted to the present-day values that guided warfare. These two texts in particular balanced very well, with Vegetius emphasizing logistics and planning, and the Aeneid celebrating charisma and leadership, based on piety and an acceptance of fate (which ended up being two celebrated values of the early middle ages). The Roman supply chain and the pantheon of the Roman gods were both dead and gone, but planning and piety could both be recontextualized to meet contemporary needs.

And just as important, there was a social function to these books. Knowing a few tidbits from Vegetius might get you into the in-crowd at Lothar's table, just as a few witty quips about Clausewitz might win a post pouring coffee at the Pentagon. Learned authors could drop lines from these texts to prove just how learned they were, or maybe even to test their readers' attentions. Expressing a modicum of knowledge about Vegetius or the Aeneid was a sort of an unofficial certificate in military strategy that other people could easily recognize.

So it wasn't so much the texts themselves but knowing how to interpret them—both practically and, in a word, politically—that guaranteed their importance. In the early middle ages, at least, interpretation was often much more important than the text itself. The dissonance between medieval realities and the classical texts they used demanded a good deal of interpretation to make them meaningful.

In a way, this might be the key to Clausewitz's success. Clausewitz was reacting to and reflecting on the Napoleonic wars, when conscription and democratic nationalism had just recently transformed the stakes of state-organized violence. But modern warfare kept changing quickly due to factors of technological change, economic mobilization, and the democratization of international politics. The world of Clausewitz has gone the way of the Roman gods, so if we are to read Clausewitz today, we need to read beyond his most straightforward pronouncements and question the assumptions he was making and the priorities that he was using. In short, we need to recontextualize Clausewitz's advice and priorities to meet our own needs. And we use Clausewitz because he already belongs to the in-crowd of the military literati. Name-dropping Clausewitz gives us an instantly recognizable basis of credibility that, say, Jomini typically does not.

So On War is absolutely a useful text, if it's read with an agile mind and a sense of Clausewitz's place in history—just as medieval readers treated Vegetius and the Aeneid. But whether the other books you list can be just as useful, I suppose, depends on your own attitudes toward reading. If you can deal with the cognitive dissonance and remain attentive to the fact that each of these texts arose or arises from its own particular contexts, you're probably doing it right. Or, at least, you're reading them as a historian might.

TLDR. Are these texts useful? Yes. But it depends on how you use them.