I fast travel basically everywhere and I don't think there are an overwhelming quantity of dragons. They could certainly reduce the spawn chances on fast travel but I think people's perceptions on this are off, tbh. After you've played the game for a long time, the dragons are more memorable than a lot of other stuff, and it seems like there have been dragons constantly when in fact you've played so many hours that it is a pretty reasonable amount of them for all the time you've put in.
Possibly, there just seems to be a theme that those fast travelling a lot seem to complain about constantly bumping into dragons. But at the same time, I've seen posts where they've fought 12 dragons in 25 hours, more than triple those I've encountered. It could just be completely random I guess.
Its also possible that the probability of bumping into a dragon is linked to your progress along the main quest line perhaps? Just a theory. I've not completed the Jurgen quest yet after 30 hours and thats pretty early in the timeline I suspect, and so not bumped into a lot of dragons. That would slightly link itself to fast travel in that you're more likely to have progressed further in the main quest if you fast travel.