The gear and composition issues are things can that can be fixed overtime and worked around.

The biggest possible issue is the server latency/systems issues that are currently hindering PvE. For instance, every melee at some point in their PvE adventures has come across the situation where even though they may be standing on top of a moving mob, boss, or anything, they are unable to hit it because of the server/client delay, rendering them unable to attack it while it is in motion.

This problem would be catastrophic in PvP.