This thread is like arguing over how many hairs must a man have left in order to be considered bald, or at what specific frequency does orange become yellow.
While i agree with what you're aiming to say, i just don't understand how you've come to the conclusion that this means that this thread is pointless.
Humans have always had an incessant need to categorize and define everything they observe, and while this can sometimes be difficult and even lead to awful results (sexism, racism, bigotry etc...) there's a reason why people always do this, and it's because it's practical, it gives our small, inflexible and fragile brains a chance to attempt to understand reality and learn how to deal with it.
You said it yourself, "it is us who inform the dictionary and not the other way around" and i think that's exactly what people in this thread are attempting to do; "RPG" is just a concept, it's not some easily observable phenomenon that you can study, so it is up to people to define its meaning and update that meaning according to how it changes through time and how RPG games evolve.
For me personally i think Dark Souls is obviously an Action/RPG hybrid since it incorporates elements that are generally associated with both genres, but some people disagree and that's fine, having debates about what defines an RPG is only natural in a forum called RPG Codex.