I know I have soloed a lot of monsters so far and have defeated most of them but that was because they are predictable and they are easy to defeat plus, I am also allowed to kill them which makes things easier. As for fighting the dragon, although we have to defeat the dragon, we cannot kill the dragon as that would also ruin our purpose of fighting against him. So for starters, it's pretty hard to hold back a lot. It's not like we are not taking this seriously but to fight a dragon without accidentally killing him? That is pretty much a troublesome thing.
Especially for me. Some of my attacks are pretty much fatal to use so I have to hold back and instead, I turned to the support side to everyone as that is the easier task for me. As for the damage output, Sigma and Harmless Sparrow just made it just right for the damage to sink in yet not kill him.