I would argue there are two things at play at here with Holiday's writings. One is as usually happens with thinkers, taking the ideas of a thinker that came before you, and then reinterpreting them in your own way, to fit your own thinking about the world. Sort of what Plato did with Socrates. Holiday took the ancient thinkers, but especially focused on how they were already filtered through by Pierre Hadot. So here Holiday was taking older thinkers and reinterpreting them in his own way, using filters proposed by other more recent thinkers. He especially stripped off all the pantheistic and cosmos trappings, and focused more on the practical aspects (and secular). It's sort of what happened with Buddhism and Taoism in modern times. What people think of Buddhism and Taoism now are just modern versions, stripped of all the traditional, religious, and ritualistic trappings of what were throughout history actual religions. Some people might criticize that, while others are attracted to exactly these stripped down versions.

The other thing at play here is a distinction between theory and practice. Seneca was a great theoretical Stoic, and his writings have lots of wisdom. However, they are most likely much divorced from practice and his actual life. After all, Seneca was one of Rome's richest men, and an advisor to Nero. So basically, in a way the Silicon Valley entrepreneur or Wall Street banker of his day.

And here I would also like to introduce the concept of utility. How much of the Stoic teachings are useful to normal every day life? Of course, this differs on the person. One person will find value in one thing, while another in something else. Take what is useful and discard the rest. For example, I learn a lot from your writings. However, not everything I find practical for my own life. So from what you write, my takeaways are piecemeal, and probably differ from other readers. However, they help me. And I think this is where the utility comes in. Reading, interpreting, learning are all acts of value extraction. You extract what you find useful and applicable, and then forget about the rest. This is what I do with philosophy in general. It might not be "real" philosophy, but it is more practical for my everyday life.