Warning: long post incoming, trying to be helpful 😁
I assume you are dieing on waves in higher dragon/dungeon stages, and not the boss fight itself... Yes, Dragon should be your main focus right now, to push to stage 20 and comfortably farm it. And Clan Boss.
Miscreated Monster would be a decent multi-purpose choice for your level (although not the easiest champ to build with low gear choices) - Ally protection, shield & crowd control (stun/fear). Provides value in dungeon waves, clan boss, and some help in spider.
That being said, progressing too high in spider is unlikely with your current roster, as brute force doesn't cut it anymore at some point without good gear. You will be looking for aoe hp burn and enemy max hp to further your progress.
Having a reviver would help, so Tagoar is another obvious choice -- speed, shield, revive, heal.
My last point would be Decrease Attack debuff, I see 2 choices: Tayrel or Aox. Even though Aox does it AOE (and he's great in CB), my vote goes to Tayrel, simply because he's easier to keep alive, also brings damage, Decrease Def and some CC. And, decrease atk on A1 is good value in CB.
Maybe I'm missing something, but I don't see Loki as a priority, as I don't see him shining in early-game. I would book Ninja as legendary priority 1, for 2 reasons: AOE Freeze = more control and a great dps.
TL:DR version: my Dragon choices would be -- Ninja Kael Tayrel Tagoar Miscreated or Ninja Kael Tayrel Apothecary Miscreated. Control and support, over brute force when not having good gear :) Of course, you should ascend them and get their masteries.
But it all comes down to how you build the champs, reaching some decent stats (not helpful if they're too slow, die from 1 hit or can't land their debuffs).
- Tagoar -- high HP, high speed
- Miscreated -- enough accuracy, decent speed, 100% crit rate, high HP, def
- Tayrel -- enough accuracy, decent speed, 100% crit rate, def, hp
- Ninja -- enough accuracy, decent speed, 100% crit rate, some survivability (hp+def)
- Kael -- enough accuracy, decent speed, 75% crit rate, some survivability (hp+def)
You will notice I said nothing about nuke stats (atk/def/hp and crit dmg). Sure, ideally you want those too, but you are early game and severely limited by gear. At this stage you really want your team to survive, more than nuke fast. A dead DPS = 0 dps, while a DPS built with survivability will still give some damage, albeit less, by being alive :) So give them HP% / Def% chests and survival accessories, if needed. Switching to nuke builds will come later on.
Lifesteal, Perception, Speed and Accuracy sets would be your best bet. And remember: stats over sets.