Reds don't look as impressive as their Elven counterparts. Elves have a lot of in-game value, and they can also chain their abilities across multiple units. It gets tiring to fight them!!! From the very first turns, the enemy's troops will start dealing heavy damage... And against units without protection, it's even worse! In my opinion, Crystal Dragons are much more useful than Red Dragons.
Added 4 minutes later
Crystal Dragons are an upgraded version of Elven Dragons. It's just that the translation in the game is probably bad.
Bow down and hear our cry,
Our earthly rulers falter,
Our people drift and die,
The walls of gold entomb us,
The swords of scorn divide,
Take not thy thunder from us,
Take away our pride.
G.K. Chesterton: English Hymnal