I don't see why having 5 people instead of 4 would make things easier, less frustrating, or anything else. The ONLY thing it would change would minimally reduce the wait time for DD's in duty finder. Everything would have to be rebalanced completely, from the amount of adds popping, to their amount of health. They would need to rebalance considering that the party has the same amount of tanking capabilities and healing capabilities while they now have 40% more damage output. (not saying 50% cause the non-DPS are also dealing some damage).

Once you get to 50 you get to do some 8-man stuff. Duty Finder builds 8-man parties exactly as if it was 2 4-man parties, so 2 tanks, 2 healers, and 4 DD's. Everything is doubled, and so can the amount of adds and stuff like that.

Just explain why having 5-man content would make any difference in how you wipe twice per instance? Maybe it has nothing to do with the balance or the amount of players in your party, and everything to do with how you (not yourself, but the party) are approaching the dungeon. Practice, learn how to not wipe, and you will always have time to complete your instances.