Since Armor was no longer providing a deflection bonus so to speak, it came time to replace armor class with a different score, simply named defense. Defense was dependent on the characters level as well as the relevant attribute (Dex, Agility, Reflexes etc.) and as such scaled nicely with attack bonuses. However, playtesting soon showed that the combination of a few abilities could allow Defense to skyrocket making it nearly impossible to hit. Those lucky monster that could hit then had to punch through the character's damage reducing armor.
This realization led to three things, first when changing major game mechanics many an ability need to be reevaluated. Secondly, I decided to scrap attack and defense being on two different progressions of BAB and Level respectively. Both would be dependent on BCB, or Base Combat Bonus which would be a default stat added to any attack, defense, or damage roll. Lastly, I realized that if the player character were to receive a double dose of protection from attacks, namely defense and armor, then it suggests that neither of these should afford such protection as to invalidate the other.
I decided that since armor was readily available to most character types that it take a priority over defense. Characters who wanted to prioritize defense would certainly be able to but they would need to invest character resources to do so rather than have it by default. This was accomplished by setting BCB to increase every other level rather than every level. By halving level based attack and defense bonuses other bonuses to attack such as from attributes and feat choices would have a more significant impact proportionally. This led to more attacks landing which see's armor getting more use while simultaneously lessening it's impact since HP was decreasing at a more frequent pace restoring the fear or mortality in my players.
Defense went through another batch of other changes but I'll get to that in a later post.