[@Psyker Landshark] at minimum, every rider has to be strong enough to make a dragon think twice about looking at them as prey or being lower on the totem pole. So for a mage, they'd need to be able to use their magic to defend themselves from a breath attack or show that they're no push over. For example, raising a wall of earth to block flames or casting a blast of fire just as powerful as a dragon's.

The most powerful mage, the empress of Avalan, would be capable of summoning natural disaster like floods, earthquakes, hurricanes and firestorms. Most others would be anywhere between that to only being able to levitate a piece of paper.

As for the rarity of riders, it depends on where they're from. In the Kovosian Empire, almost everyone who is a mage or awakened will try to become a dragon rider since it's so central to their society. In the west though, the process is less centralized so while some may train to become riders from an early age, others may develop their skills first before thinking about becoming a rider.

In other words, those from the east tend to become riders as early as possible (basically as soon as they meet the most minimal requirements) then build up from there, while those from the west tend to develop their talents first and then go on to become riders with an already strong base of skill in mana or prana. Some may even choose to not be riders at all.

Another thing to consider is that there's only so many dragons to go around, especially those mature enough to be useful in combat. In Kovos, there's enough to form an entire fleet of riders with their numbers being in the hundreds. The 3 nations of the west however had to form the Alliance just to match those numbers and yet still fall short.

Hope that answers your questions. Lemme know if there's anything else you'd like to know.