Elder Dragons have three distinct features that distinguish them from other monsters;

1: they can cause an inexplicable phenomenon of some form or another (Teostra/Lunastra Cause heatwaves, Kushala causes hurricanes, and Chameleos can create nigh un-navigable fog-banks)

2: other monsters naturally respect/fear them (in the old world, the small monsters hang around, the map is completely devoid of life save you and the Elder Dragon)

3: they all can control the dragon element to varying degrees (at least in older games, every last Elder Dragon had Dragon element imbued into at least some of their physical attacks, even if it didn't proc Dragonblight.