Of course, theres also the fact that The Loyal Three (and their leader, Pecharunt ex) are all great cards in general, which does help
And Rin and Seri can tap to deal damage equal to the number of Cats and Dogs you control which adds up fast
What if your blockers get smaller after combat, even if you did manage to find a profitable block
Starting with the Alara block, booster packs for both Core Sets and expansions began to contain 1 land, 10 commons, 3 uncommons, either 1 rare (7/8 chance) or 1 mythic rare (1/8 chance), and either a tip card (which explains the new rules in the set, such as exalted in the Alara Block or Infect in the Scars of Mirrodin Block) or a token (which is of a type produced by a card in the set)
The beauty of Colorless is its simplicity - no type advantages, no restrictions, just pure adaptability