Open world PvP has never been balanced in any game - there is a reason you can't have 7 people in a game of chess.
In LOTRO because balance patching only happens as part of larger updates, there are massive shifts in balance followed by a slow change over time as freeps continue to improve their equipment until a new update is released. Creep side sadly does not get the benefit of gradual improvement as you have the skills you have and that is the end of that. In an open game you can't achieve balance between factions in a 1v1 fight and a 50 v 25 fight, one of the two will always be lopsided.
I think a really good demonstration of how much time and effort goes into PvP balancing and creep side development especially is that the official stickied threat of creep roles still only features 5 of the 6 creep classes.