This comment from one of the guild leaders of a worldwide top raid guild:
"im yet to see a rogue switch his agility gems for armor pen because of an encounter or their own thought process.
if they do change it, it's because some spreadsheet says it's now the best way to do it and it's completely pointless ... the actual number of people that properly understand the maths of stuff like armor pen is TINY"
I myself have wondered how many people on EJ actually have a clue, and how many are more like me "tell me what works".
As Tobold mentioned how restricting being able to choose any number of skills would be, we'd all just pick whatever the best choices are at the time.
I've also pondered how many guilds actually work out content on their own? And how many of us copy what we've seen done elsewhere?
10 hours ago