Many terms and frameworks evolve beyond their original intent, so I'm not too worried that this has evolved, too.

I've always found it is easier to understand servant leadership as the opposite end of the spectrum from autocratic leadership: Is the leader primarily concerned about growing their own power/success, or growing the power/success of those who work for them?

There is a lot of middle ground between those two extremes, but without that contrast in mind, you can easily lose track of what the terms mean. The article does a decent job of trying to find a healthier middle ground, IMO.

The problem with servant leadership is twofold:

Firstly, in 'proper' servant leadership as taught by Greenleaf the leader is supposed to put the church before their own needs and wants. It is not about serving the people who report to you; it's about serving the organisation first. In a business context that's horribly toxic and a great way to spend years being exploited by a company that will grind you to burnout for very little money. Thankfully most people don't actually follow what Greenleaf teaches because they think it's about the people.

Secondly though, people don't bother to read much about it. They hear the term and a basic summary, and then fill in the blanks based on their own biases and assumptions. Consequently when someone says they practise servant leadership you can't know what they mean unless you know them well. People who practise their version of servant leadership assume other people mean the same thing by it, and automatically align themselves with that person based on (probably) false assumptions. It is not a helpful term because it's used for a huge range of leadership styles.

The problem is when things evolve we no longer know if someone refers to the evolved form or the original. Or more importantly if the evolved form retains the important parts of the original.