How do you design content around flying? Flying is inherently limiting in gameplay possibility. Other than flying through hoops in the air, there's no trick to it. You mount, fly to the mob you need, divebomb it, mount again, repeat. Without flying you can even design a quest to just enter a fortress and get to the other side of it while fighting your way through or avoiding mobs without having to have a quota for how many mobs you need to kill on the way. Removing flying opens up so many possibilities and adding flying adds none.