Early dragons (1e/B/X): they might look weaker by the numbers, but so were the characters. And they were encountered at much lower levels. A 9th level party could expect to see an ancient red dragon. Breath weapons were 3x a day (so you could do 3 rounds in a row), and they did the dragon's hp in damage. So that ancient red dragon would do 88 points on a failed save, 44 on a made one, each round for 3 rounds. For reference, a 9th level fighter with 16 CON would have 60ish HP, a 9th level MU would have the low 20s in HP.