It still hurts defensive builds, though.
Depends. If they're really low on damage per attack, then armor-as-DR is worse, but if they have moderate damage per attack and a poor attack roll (so they're not hitting more than once a round at high levels), then it's worse for them than armor-as-DR.As for high-AC low-DPR fighters, this is better for them than armor as DR at least, as here their damage stacks with everyone else's for bypassing armor, with DR they lose a much larger chunk of their damage than everyone else, so it hurts them more.
Only because casters (the most essential part of the party at higher levels) tend more toward the offensive builds, and mixed parties don't do well. If you can give me a good defensive wizard build (I already have one for druid), and ban cheese like stacking CL bonuses, I suspect I could make a defensive party capable of holding its own.but let's be honest: Low damage high defense turtles are already a bad option.