I've been in quite a few parties lately via Party Finder for Primal Ex's or Hard Instances that have requested that all recruits be ilvl80+ and "not suck" at the game. Despite the great gear most players in the party had, it ended up in epic failure many times.

So yes, OP is correct. Gear doesn't necessarily make you a great player - just helps reduce your damage and increase your DPS. It does not save you from your inability to recognize when to dodge specific actions from a boss, determine when to time your actions properly, or if you're stealing aggro.