Why did you play it that way if it wasn't enjoyable to either you or the players?
That's sort of like asking, "Why did you ride the rollercoaster if it wasn't enjoyable?" You don't know how it's going to be until it starts.
Many people would say that it was played that way because you didn't want to metagame. I would say that I have enough of "not metagaming" in real life, and I want fun in my games. Metagaming was included when you created the encounter, so why refuse to metagame at the table, even at the expense of a good time for everyone?
In the first encounter with the dragon, it breathed fire on them in the first few rounds. No one was killed that time. But they saw the shape and range of the breath weapon.
When they realized how powerful the beast was, they retreated out of the dragon's cavern and down a 10'-wide corridor. The dragon could have followed them down the corridor (Large size), but it chose not to. In fact, it wasted a whole round standing put outside the mouth of the corridor and inhaling for a breath to come next round (4 rounds reset).
2 PCs ran down the corridor as far as they could in that round. 2 PCs just moved a little ways into the corridor, but they were just barely out of the 40' breath range. I don't know if they measured the distance (in their heads) or just got lucky. 1 PC took the delay by the dragon as a chance to get in another spring attack. When the dragon breathed the next round, the spring attacking PC died.
The dragon then turned around and walked away from the corridor, satisfied that the intruders were sufficiently terrified of it. Then the sorcerer, who had been missed by the fire breath by just 5 feet, went back to the mouth of the corridor and got off a single spell -- blindness -- and then ran away. The dragon failed it's save versus the blindness.
Later, after the dead PC was raised, the PCs went back to take on the now blind dragon. Unfortunately, dragons have blindsense. But the dragon was very unhappy with being blind, so it wanted to parley to get the sorcerer to remove the spell.
Now, the dragon didn't beg and plead or anything like that. It demanded and threatened the party with destruction if the mage didn't remove the spell. The party apparently were not interested in removing the spell (where not even interested in the attempt to parley), and wanted to take the opportunity to fight the dragon while it was blind.
Unfortunately for the party, blindsense works just fine for area affect spells and breath weapons.
The dragon dispersed the group with a stinking cloud and then jumped into the fray to grab a bargaining chip. It grappled a PC and threatened to kill him if the mage didn't remove the blindness. The party continued to attack the dragon, and the PC escaped its clutches.
For many rounds, the dragon did not use all its attacks on anyone. It just used one attack to get a grapple. Unfortunately for me (trying to give a hint), the PCs didn't realize the dragon could have done more attacks. (Although one of the Players mentioned, after the game, that he knew it could have made more attacks.)
One round, though, the dragon gave full attacks on the PC most likely to survive. The PC retreated with single-digit hit points.
Then the dragon grappled another PC and again threatened to kill him if not unblinded. The PCs continued to attack the dragon. Although the dragon only used one attack (of its multiple) in the round it grappled, it should have just done nothing but hold its victim for one more round to really give the point that it was trying to pause hostilities. But the PCs were hurting it.
So the dragon did its full attack options on the grappled PC and tore it to pieces. The fight continued.
Then the dragon got ahold of another PC and held him over some lava, and threatened to drop him in if the mage did not remove the blindness. The other PCs continued their attacks, and the grappled PC tried to escape. (I don't know where the grappled PC thought he would go if he got free -- he was hanging over a pool of lava.)
The dragon dropped the PC into the lava. (I gave him a ref save to throw himself on the edge, but that failed.) PC took 70-some damage and was gone.
More attacks on the dragon. So the dragon moved up and breathed on two of the remaining PCs who were grouped together. They both died in the fire.
After a few more rounds, the last PC standing (with only a handful of hit points remaining, himself) managed to kill the dragon with spring attacks.
Note also, there were also 4 minor critters in the dragon's cavern. They were not much of a threat to the PCs -- they did minor damage (if they hit) and the PCs killed them with one attack each.
I had pulled the dragon's punches a great deal. For many rounds, the dragon made just one attack or just grappled and held instead of totally going whirlwind of death on the party. But I guess I was being too subtle with my hints. One Player commented after the game that if he were the dragon, he would have grabbed a PC and flown up out of reach and then tried parley.
A simple potion of protection from fire for each PC would have saved even the one dropped into the lava.
I am curious what the driving force is to play a game that is not enjoyable.
The expectation/hope was that it would be fun. The result turn out to be not enjoyable.
Bullgrit