Comparing them to Flygon is like saying Gyarados and Milotic are the same, because they have the same general typing and move pools.
Quick question...have you ever used a defensive gyarados before?
Anyways, flygon's power in uu is almost unrivaled due to the offensive pace of the metagame, and the fact that it has the moveset to make quick work of dedicated walls and sweepers alike...mostly it boils down to either being a physical-band, physical-scarf, or mixed -scarf set...they're all darn good sets for different reasons...all in all tho, you're usually gonna see sets that have a dragon attack, earthquake, fire attack, and either u-turn/roost/auxilary dragon attack...that's all you have to look out for...so that means that you'll only need a little bit of prediction, and the right sort of team and you'll be ok...or you could just slap a scarf cryogonal on your team and call it a day