The flight was not available to everyone. It wasn't greatly affected by strength, rather, it was abilities, equipment, or the construction of the body that mattered.
Birds didn't need engines like fighter planes to take off, they only needed their low weight, the structures of their wings creating air pockets, and a bit of experience.
The same was true for monsters. The White Threat Monster could easily be able to fly, it wasn't unusual, and it didn't necessarily give any advantage in battle. It depended on the specific situation.
But, flying was useful in covering a long distance in as short a time as possible. Moving through the air was much easier and faster than on the ground because there were no obstacles up there.
For most Lords, this wasn't a problem. Even if they couldn't fly or have the necessary body parts like wings, they could use their energy to do so.
