Perusing both martial arts and combative systems over the years, the difference between Practical vs Principle-based, and Real vs Research, has struck me as one sometimes not recognized by practitioners and commentators.
I feel we most often see the error on the Principle based and Research side of the equation. That is, training practices, exercises, drills, even the bulk of a discipline, much more about exploration of principles, playing with energy, working with structure in various ways being mistaken for practical and realistic fighting methodologies. This is not to say that some Principle and Research based stuff may not be directly practical.
Unfortunately, when the difference is not recognized, this serves to dilute the credibility of the art and/or its practitioners. When people are touting what is obviously more developmental exercise or practice as "realistic" there is a tendency to dismiss the art and "throw the baby out with the bath water."
For example, there is plenty within BJJ that is by no means street practical, or competition practical, on various levels. But I would not look at something like "flow rolling" or the various cooperative drills we do and say "see, this is practical fighting application."
Steering clear of specific arts, what and or how do people go about telling the difference between what is practical and realistic and what is more "research and development" oriented in what they do?