Make dragons really hard to kill. Risky

Make it so dragons deals extra damage to isolated targets. Give them some unpredictable aoe dmg. Give the dragons the ability to move around the map and leave the burning trail behind that ll dmg on the path every time it breathes fire on the ground.
Make it so the dragon can actually punish the team for not killing it within some.set time. Like by making it kill the monsters in the jungle or by spawning dangerous monsters with agrroo system on the river by making it harder to gank.