Well let's say both sides have dragons, and infantry and cavalry etc.
The infantry and cavalry would fight each other on the ground as will normal warfare. The Dragons being predominantly airborne would engage in 'dog-fights' between the enemy units. Although trying to harass the ground troops, doing so would make them vulnerable to their enemies dragons.
I wouldn't say the presence of dragons would change the tactics of the Roman army or render it's forces inept. Instead they would be prepared for what they might face, their own dragons would be on reserve to protect against air strikes.
The infantry and cavalry would fight each other on the ground as will normal warfare. The Dragons being predominantly airborne would engage in 'dog-fights' between the enemy units. Although trying to harass the ground troops, doing so would make them vulnerable to their enemies dragons.
I wouldn't say the presence of dragons would change the tactics of the Roman army or render it's forces inept. Instead they would be prepared for what they might face, their own dragons would be on reserve to protect against air strikes.