The dragon should win this fight every time. I know from experience.
The climactic battle in my group's first 4e adventure had them face a 3rd-level hob commander, two 2nd-level hob soldiers, and a full strength (4th-level solo) young black dragon.
The party was all 1st level, no magic items, with a human ranger, human wizard, eladrin warlord, human paladin, human cleric, and dragonborn fighter.
I wanted the encounter to set up Xarr (the hob commander) and Rixidirix (the dragon) as the long-term nemesis to the party.
The encounter started with the party fighting the hobs, the commander getting bloodied, retreating and calling in the dragon. The dragon is ordered by the hob commander to fly him the heck out of Dodge.
As soon the dragon came onto the battlemat things went downhill for the party very, very quickly. The paladin was dying at the end of the third round, everyone else was bloodied or close to it, scrambling for surges and burning action points. The dragon had been hit maybe a couple times and wasn't anywhere near bloodied.
Why did the dragon leave the fight? 'Cause the cowering hob commander told him to. Why is a dragon taking orders from a hob? That's what the party wants to know too!
Even though the party got their asses handed to them, they were all super excited to encounter a dragon at 1st-level.
I think that's the real lesson. It's okay to have encounters that will result in TPK if fought to its end, but as DM you should have escape valves to keep that from happening (as long as the players aren't stubborn idiots, that is; nothing a DM can do about that).
It might have been a closer fight if they were fresh, but that's a poor way to use a solo encounter, IMHO.
This encounter brought them to Level 2. But the fight wouldn't have been much closer without some help dealing with the dragon's magical darkness. That's the real killer; swinging wildly in the dark--and the -5 to hit that goes along with it--is never a great strategy.