User blog comment:Kogath/Monster Hunter: World Discussion/@comment-25083735-20191105005322/@comment-31029678-20191110120333

If it was just a matter of power then creatures such as Akantor, Ukanlos, Deviljho and Rajang etc.... would have already received that classification ad kept it for all this time, they are powerful and they definetly affect the enviroment. We know devs care about classes and they follow some rules for that, "recently" they fixed a mistake by re-classifying Gajau from Piscine Wyverns to Fish.

In World we also got the hint that an Elder has to have a natural blue-bioenergy. And if we want to bring in Frontier in then they have to possess that specific kind of blood.

Again, there's clearly something going on with how Elders are classified, as much unrealistic it may seems the "they are related" idea does answer all the questions, why they all stand outside of the regular animal kingdom and why they share the same blood whose mysterious ingridient probably is connected with the blue bioenergy. That ecologic tree then surely help that idea... though we should wait for the next one, after Gen5 and a major focus on the story they may do some retkons to clarify stuff once and for all.