FrogReaver
The most respectful and polite poster ever
I don't think it's difficult. It just means the whole team has to invest into boosting their own personal defense before it really pays off. It's fairly easy to invest in personal defense though. Casters can multiclass to a class with heavy armor or medium armor and shields (plenty of choices for that).That's very true. As a DM I assume intelligent or cunning creatures - with experience of combat and whose lives depend on it - will circumvent the heavily armoured defensive types. Another example of the difficulties of designing effective defensive features.
Martials can invest into Barbarian Rage or defensive spells.
Maybe. I'm not sure that activated defenses are particularly more interesting to me or even powerful enough to take. Look at feats like defensive duelist or the battlemaster parry maneuver or the monks deflect arrows. All are activated options that you rarely see picked or used.Sure, but - to my taste - these broad, always-on defenses are the least interesting.
I think this is one area where people focus too much on relative impact instead of absolute.Were you inclined, you might investigate via probability distribution functions the efficacy of blur in conjunction with decent armor. Yes, it uses a resource. It frees up more resources, however.
As an example, take a character getting attacked 6 times in a combat with a 50% chance to be hit. On average he will take 3 hits. Blur would reduce it so that he takes 1.5 hits. That a 1.5 hit difference.
Then look at an example of a character getting attacked 6 times in combat with a 30% chance to be hit. On average he will take 1.8 hits. Blur would reduce it so that he takes .54 hits. That's a 1.26 hit difference.
Point being, blur isn't actually preventing alot of hits in most combats.
True Scotsman, meet Whiteroom StrawmanA true Scotsman is a noble gentleman.

IMO.The two strongest fighting styles are archery and defense. Dueling is third. However, you will consistently see the damage overrated.
Archery is the best for archers.
Dueling is the best for sword and shield.
Defense is the best for Two Handed Weapons.
It's a tie between dueling and defense for combat with one handed weapon and a free hand.