Most players play every day to win their daily quest. Most daily quests involve winning in PvP matches. Thus, many players end up bottom-feeding: they keep their PvP ranking low so as to win more easily and complete their daily quest faster. That's why 90% of Hearthstone players are below rank 10 in ranked mode.
To reach the number of wins for their daily quest faster, players may want to concede and start another game when they see they have no chance in the current one. There are several techniques to gauge an opponent and the likelihood to lose:
- A golden hero protrait indicates the player has won 500 games with that hero. It is a veteran player, most likely with lots of good cards.
- Decks composed of 4+ legendary cards, especially Sylvanas, Dr. Boom, or Alexstrasza, are from players who spent a lot of money.
- Purchased heroes means the player has certainly spent a lot of money on card packs as well.
- A legendary card back indicates the player was dedicated enough to reach the top .25% of the player base.
- Old card backs indicate the player is a veteran, and must have good cards.
- Heroic dungeon card backs are awarded for clearing a dungeon in heroic mode, which requires many good cards.
Having players with different skill levels playing together is problematic. Veteran players tend to have better cards and more skill than beginners. As a result, beginners may frequently go on long loss streaks. Loss streaks are very unpleasant, and come to mind faster than win streaks. So when players talk to their friends about Hearthstone, they are more likely to complain than to brag. That won't encourage their friends to start playing.
There are solutions to bottom-feeding. One solution is to pool beginners together so they don't get beaten up too quickly. Another solution currently in place in Casual Play, Tavern Brawl, and legendary-rank games, is using a ranking hidden from players such as MMR. Hiding player's rank from them prevents them from knowing where they stand, and the average skill and cards to be expected from their opponents. But players can easily cheat the system and drop their MMR by conceding games before they even started.
A great solution would be to consider both the player's ranking (as is currently the case) and the rarity of the cards in their deck. In fact, websites listing Hearthstone decks already take into account the rarity of the cards in a deck by providing a dust cost. Epic and legendary cards cost a lot of dust, and are either useless (and therefore unused), overpowered (and therefore always used), or the keys to unlocking synergies in a deck (which is where the game is interesting). I think it would make sense to at least take them into account when matching players together.