Are they though? As noted in story, Courier Weight dragons are fairly dumb.
They are dumb relative to humans, they are still able to talk and actually form sentences, they are definitely sapient and that makes them MUCH smarter than any predator humans have dealt with.
And Dragons aren't that armored. They're not more armored than say, Elephants or Rhinos and those got hunted enough to develop evasion behaviors to not die, never mind the non-African Megafauna that mostly just died.
1)They are armored, except for some vulnerable spots.
2)Conceding for the sake of argument, Elephents and rhinos were hunted using pit traps because humans did not have any weapon that could reliably kill them. Other methods of killing them relied on poor senses and using fire to herd them into a suitable killing ground. Needless to say these methods will not work on Dragons.
3)Even if we assume that a prepared group of hunters would be able to kill a dragon, the point is that dragons can fly - they won't be attacking the prepared group of hunters, they'll be attacking the camp, and mon't be leaving tracks for the hunters to follow.
4)Dragons can fly hundreds of km. If the dragon's lair is 20 km from the
Dragons don't have long ranged weaponry so
THey have better long range weapons than the humans do in the time period we're discussing. They are more than capable of throwing, or simply dropping things on people.
Roads are pretty much as safe as they were IRL for the same reason as IRL, humans destroy the competition that won't stay away.
THe difference is, humans were able to outrun any animal they needed to worry out, and track down their lair.
The communication thing sure, except not really because guess what, Dragons can't hold territory and newly tamed Dragons are, once again, too small and lacking ways to deal with ranged threats to be more effective than say, Cavalry, but Cavalry doesn't have to worry about big ass wings. Dragons would be PART of the Legions/Auxillaries, but the ones doing the bulk of the fighting would still be the Legions.
Dragons aren't needed to hold territory, but they can be used to launch punative missions against anyone who doesn't follow orders.
Geography is still the same and the vast majority of pressures are still the same.
No, even the geography is not going to be the same, you have dragons which are valuable, that means the roads will go different places, the information people have when setting out to make roads will be different, and of course, weapons technology will be radically different.
Heck, once dragons are domesticated you'd get spices delivered from China to Rome in a couple of days by riders who actually visited there, that's going to have a huge effect on society.