At least you earned good loot for it. Guiding Longbow isn't exactly a rusty helmet right?

this had been reported before and I thought it had been fixed. You sure your game is up to date?

Well it was still a dragon. Even a level 1 Dragon is a thread due to flamebreath.

(I encountered this in the scenario as well)

the dragon in the screenshot is level 12 and it has 270 HP, which is also consistent with the level. that thing should definitely give more XP, even with two heroes in the attacking stack. the heroes are level 9 and 10, so they should probably even get bonus XP for defeating the dragon.

the dragons (the proper dragons, not lesser slags/forest drakes/drakes) all start at level 12 as far as i know (+bonus levels if playing higher world difficulty and/or the event that increases all monster levels)

The XP formula overvalues levels, pure and simple. The creature type has different starting hp, attack, defense, and skills, this is the lion share of difficulty. Levels make a paltry difference compared to creature type, but are a huge factor in XP. In at least 90% of the cases you if you can beat a monster then you can beat the same monster +4 or more levels just as easily (if you played a summoner and maybe tweak your +summoning levels, you can get a feel for just many levels it takes to make much of a difference). The only cases where this tends to not be true is with troops because HP is a huge deal on troops (unit size), and heroes because their levels bring new abilities, but heroes and troops give practically no experience anyway.