So, let's suppose I finally made it. A creature that's very agile, able to resist most small-arms fire and has a whale-oil breath weapon. Flight is solved with bones, as strong as carbon fiber, (laughs in limpet teeth) and even more muscle on the pecs.
This example dragon's name will be.. Gyvaris.
Now, the dragon also has a rider... which leads to a few problems, namely:
The dragon simply can't use active flight to gain altitude with that weight on him.
This isn't a problem if he's to take off from a ledge or any similarly high place, but that's not always possible.
Sometimes they're forced to land in places where dragon and rider can't take off, so usually only the dragon does. Dragons are more vulnerable on the ground, so it's better that way, however, now the rider can't catch up to the dragon. An ODM gear (if possible) would still be close to useless in, say, a prairie.
I've no idea how a dragonrider could catch up to their mount on land, and with lightweight gear, do you have any?
Why can't a dragon take off with a human?
Note the Quetzalcoatlus.