I've posted about this numerous times, but after doing a lot of research I've had some eye-openers.
"Damage scales more than Defense, so defensive stats are mostly useless."
This appears to be true on the surface, but actually isn't. Defense is only two stats that are weighted more or less equally, while (power) offense is three stats with distribution significantly weighted toward one of them (Power.)
So the real contest here is to look at Berserker's vs Soldier's and see what the tradeoff is in terms of damage and defense. This spreadsheet does exactly that:https://docs.google.com/spreadsheets/d/1xXxJl1yTzgVeeLtOdPpBk9nWyXmyhvJ1hGcEtnQ1H34/edit#gid=0
Berserker deals around 50% more damage than Soldiers, but has less than half the effective HP. Combining that with healing skills and dodging, this means that defensive stats are actually a lot more effective than people believe them to be. The key thing to remember is that you never want to sacrifice Power for defense unless you're full condi or playing a full support build in a group. But taking some Toughness/Vitality instead of Precison/Ferocity actually isn't a bad tradeoff even in PvE and especially for solo/open world builds. People love to say "get gud and dodge moar", but this is kind of a brainless meme. If you're playing solo in the open world and regularly engaging multiple mobs - you'll eat plenty of hits. Bolstering your defense even a little bit can help you maintain battlefield control and makes it much less likely you'll get downed. The other thing that people seem to forget is that, while mastering dodging is very important, it also interrupts your outgoing damage. This means there are a lot of circumstances where absorbing damage is more efficient than dodging. Vitality + Toughness allow you to get away with doing that a bit more.
This is why so many sets have Power primary. I think making a Berserker primary with some Soldier or Valkyrie pieces mixed in is probably the best way to play Power in both PvE and PvP in many cases (yes, better than Maruader's) - you sacrifice no Power while having a healthy mix of Precison, Ferocity, Vitality, and Toughness.