Both Artak and Corvis are excellent. You defeat dragon through debuff-based damage (poison or HP burn), not direct damage. Corvis even supports Artak with his debuff extension.

Make sure both of these have around 150 acc. They should be able to do the job even at lvl 50.

(Also, I kind of disagree with lots of youtubers here, but speed isn't that important. Speed boots are nice, but by no means necessary early on. Make sure you go faster than the enemy. Beyond that, it takes a lot of speed until you start to see the benefits)

high khatun can bridge a gap most people are missing in early/mid game with her lead aura and also added increase speed/tm boost, can also make a large difference in CB etc to, and for what u need her for at the moment she will probably work at 50 quite comfortably, as for the dragon lair 13 just avoid the fight with the dragon specifically going for 5 + mins because it hits harder each time it casts so you will eventually get nuked if u take to long, as others have said just hit it down with psn stacks and burns. primariliy psn stacks.

also try to acend ur champions if you can, each acend level will increase the basic stats of ur champs, every little helps.

IMO your problem is that you need to focus on getting those legendaries to 6* before you focus on farming dragon. Doing so will also allow you to progress further in Faction Wars, which will get you materials to forge Perception gear, which is better than Accuracy gear.

Thank you guys / @Fathertron and @oblivion01332