I’m not going to comment on how Ranked matchmaking works; there are a number of threads speculating in that direction and it’s general anecdotal observation… and guesswork. Instead I notice you mentioned:
[quote=“DragonDai, post:1, topic:18837, full:true”]
I have leveled 2 cards one level (to level 2) and one card to level 20 (the one Mythic I pulled). I have also put a couple of level 1 traits on a couple of cards and have exactly one card with a level 2 trait as well. On top of this, I have ascended everything every chance I’ve gotten. Finally, my character is somewhere between level 60 and 70. [/quote]
… that you are entering PvP using unlevelled, Level 2 troops paired with an untraited Level 20 Mythic? Oh my.
You don’t say which Mythic it is, but I think most of the problem is that the power rating of the Mythic does jack up the team rating of your troops… without adding any value to your actual team strength.
At your level, you shouldn’t be using any Mythics at all when they are untraited: Simply because your mana mastery is low and the Mythic requires way too much mana for you to cast it. At a minimum, you will require a gem transformer to help fill up the Mythic more rapidly. Examples of excellent gem transformers are Valkyrie (creates Souls & Blue) and Hellcat (creates Red and random damage).
Rather than use the Mythic, the devs have said in general that they expect most players under Level 100 to be using their Hero as their topmost tank card. The Hero classes and the unlockable weapons are quite strong in the right team.
For PvP to be enjoyable, though, your troops will have to be strong enough to withstand at least 2 to 4 attacks each. At your level it is more important for you to level your main offensive troops to at least Level 12 to 15 before taking them into play.
If you’re having trouble choosing, then think about levelling some good inexpensive troops like these (listed not in any particular order… I would choose the ones to use by color synergy preference):
Valkyrie (#1 priority)
Druid
Boar Rider
Mercy
Hellcat
Giant Spider
Soothsayer
Spirit Fox
Goblin Rocket
Herdmaster
Sabertooth Lion
Mist Stalker
Rowanne
Rakshanin
Scale Guard
Wraith
Crimson Bat
and if you have it, another blue-based damaging troop like Emperor Khorvash or Treant or Shadow-Hunter or Astral Spirit.
Your team becomes:
Hero
Blue Troop (Does damage)
Valkyrie
Support troop that cleanses/ Heals/ Does damage
If you have The Dragon Soul (TDS) you can replace Valkyrie with him. He generates mana for everyone plus he does AOE damage. Keep in mind though that TDS is rather slower to fill than Valkyrie… Your starter team could be dead before he gets off his first cast.
Choose a weapon for your topmost Hero tank that minimizes blocking the mana colors of the troops below him, and you’ll be good to go forth and conquer Krystara 
Hope that helps?