Okay, we know the type-IIb FG muscle fibers are the strongest stuff we can use. So, the only thing we can do is attach more, but how?
Dragons are 180 cm tall at the shoulders with a total neck+head length of 180 cm, a body 180 cm, and a tail 280 cm. Many of the body's bones are fused together, resulting in decreased/non-existent flexibility there. The neck is long, 2/3 of the total neck+head length. The tail and neck both use a bit of Arambourgiania magic.
Dragon bones have a structure similar to limpet teeth, so basically, goethite fibers in a chitin matrix, kinda like an organic short-fiber composite. Tensile and compressive strengths are 4.5 GPa on average, with the right fiber orientation, of course. There are some bones, I haven't tampered with, that store calcium and phosphorus.
Tendons received an "upgrade" as well, in the form of CNFs, tensile strength is 1.6 GPa.
Dragon wings are broad, soaring wings, similar to that of an eagle, reinforced with actinofibrils.
Dragons dissipate heat through their wings and during exhalation. They use their flight muscles sparingly, and never longer than 90 seconds at a time. They eat fish, meat, fruits, and algae. The primary mode of flight is soaring.
They have six limbs in total: 4 legs and a pair of wings, sandwiched between, just far enough not to interfere with one another.
So, I guess I'll have to pack additional muscle on the keel (mainly because of the extra pair of legs), but I want to pack it in a way that power output increases linearly with muscle weight, how can I do that?
I do know that the force, muscles can exert, is the function of cross-sectional area, if that helps.
Figure time: I originally gave dragons a wingspan of 11 meters and a width of 2 meters. So, the dragon could be 11x2x20=440 kg and have the wing loading of the Quetzalcoatlus northropi. I'm not sure if this is correct or helpful, but here ya go.