Mokona said:If level power were linear then the same ratio would exist between the number of 1 HD monsters a 1st level party, a 5th level party, a 10th level party, and 15th level party could defeat. For example if the linear slope for levels were 1 then fifteen 1 HD monsters would the same difficulty of challenge to a 15th level party as 1 such monster is to a 1st level party. The experience award and CR tables in the Dungeon Master's Guide also aren't linear.
You're right. When you first wrote "class levels should be more linear" it was unclear whether you were talking about the bonuses, or the effective power. I'll concede to what you've just written here.