Another point: You think, that a rare is always stronger than a common card ?
Where is this written ?

Just one example:

I take to similiar monster - both tanks, one is rare the other common:

1. Frozen Soldier (rare)
2. Flesh Golem (common)

both cost 6 Mana & both have 2 abilities.

1. Magic Reflect and Shield
2. Heal and Void

OK it depends from the ruleset but if it's not "no heal" I think that the abilities of the Fleseh Golem are more usefull than that of the Frozen Soldier.

The Flesh Golem has 11 life and if he get summoner buff 12 life what bring him a nice healing of 4 lifepoints each round.

The Frozen Soldier has 7 shield, but only 6 life - so he will be killed from magic attacking monster quite quick.

If you would let both alone fight against eachother the Flesh Golem would win in (nearly) every case, but I would guess that also if you look to the game statistic the Flesh Golem is used much more often than the Frozen Soldier.

So you really think further that rare cards are always stronger than common cards ?