I'm very mixed on this as I agree a lot of C-Levels mostly have mastered the art of selling themselves and I find most announcements of new C-Levels in my company to just be a waste of an email and likely salary.

But your last part strikes me as falling to a common misconception that climbing up the corporate ladder from inside is best done based on merit, as leadership is not always compatible with the actual work being done at the lower levels.

C-Level leadership tends to be more about company growth and being able to understand which parts of the company do need to change/evolve to reach that next level, sometimes with hard decisions. I've gone up the ladder like this from a very low level to a few reports away from the CEO and definitely it changes your perspective a bit on how you approach things.

The simplest example is realizing you have a lot more decision power over how you interact with your customer base, and options like "we simply won't support this" are a viable option when before you didn't have such options. How you allocate your people towards projects becomes far different when you introduce a new product/feature, and so on. It becomes a lot less about the minutia of the day to day work and instead about the long-term sustainability and health of the people and the company. Learning to take in a larger scope of understanding is not easy and not everyone naturally learns it, yet many companies still follow the time-based seniority model or promoting to leadership persons who really don't have basic leadership qualities.

You also have to consider your top people and how to evolve your strategy without ostracizing them or causing disinterest; too much workload on your top-tier team members and you'll start to bleed such people. Same with adding in too many things not related to their interests. Ideally, in such a high level position you're listening closely to the feedback from the lower managers and making decisions that try to balance both aspects and pushing only on situations where the growth is very essential, but there in is the catch: how can you know what is essential until you try it and see the result? What worked for one company doesn't work for another as no matter how similar the product/services might be. I've seen this happen tons of times with support and RND teams that were basically modified to include professional services aspects which is not what any of those people signed up for, and there was a huge exodus. The justification was that the C-Level who made the call had success with this at another company X, but the scope of what had to be managed was far more narrow at X and the client base with a support package was significantly smaller. The results at X were undeniable, but the conditions under which such a change were effective were quite different, and the C-Level just failed (refused?) to recognize this.

Leadership is very hard to grow properly, and personally I'm of the opinion that people who seek leadership are to be treated sceptically, as it's something that grows with familiarity and organically, not in a classroom. The Classroom helps with the fundamental skills (statistics, financial studies, etc), but my personal observation is that what gets lost in these classes is that such knowledge then needs to be heavily customized to the environment you're in. It doesn't really matter how many tools you have for leadership if you're using the tools incorrectly.