Sure KE is limited like anything else that is an easy to automate metric, but I must tell you it is SUPER effective in evaluating who are the Splinterlands contest exploit masters :)
Sure, it would be nice if it took into account SPS and other second layer tokens, but as is it really measures what your behavior is towards Hive. If your KE is at 2.0 it means that you took at least 50% of your Hive rewards and put it somewhere else. That somewhere else could still be on Hive like HBD savings, or it can be in Splinterlands or Holozing assets. Those things you should also evaluate when investigating what someone is doing on Hive.
Then there is an aspect of we need more popularity for Hive and it is not a bad thing to sponsor some great authors who will just extract. If content is outstanding it might be worth it to us as Hive stake holders to overlook their extraction behaviors and just reward them for other benefits these people bring to Hive. The judgement becomes more subjective and less clear or easy to make compared to the cut and dry KE metric.
RE: KE alone is not the KEy