I disagree completely. I will be playing this game primarily as a competitive PvPer. I love the idea of tournaments, teams, etc and intend to do well as a competitive player. In a game like this I think that from a competitive standpoint you really need to know all of the classes inside and out in order to play at the highest level, and to do that obviously requires a lot of play time on every class. While I intend to main mesmer, I also intend to play every other class quite a bit and play different classes and different compositions with my team. I don't want to have to delete and create characters every time I want to play that 6th 7th or 8th class. It's going to become a major nuisance for me to have to recreate characters, setup traits, get al my gear from the vendors, rune the gear, sigil the weapons, select skills, etc every single time I want to play a class that isn't one of my 5 current characters. Maybe you consider it a luxury to play all 8 classes frequently, something that isn't necessary, but for competitive players it will be important in my opinion.
You don't want to, you don't have to. It is made possible for you to delete 1 character and make a new one and in gw2 you don't even have to max your chars to play PvP. To make your life easier you can purchase more slots for your 6th - 8th characters. And ffs guys, this is a buy to play game! You can easily spend a few dollars to get that 6th or 8th character when there is no sub fee. This is a freakin MMO and ANet is a company that aims to make profit for the investors! They won't give you the moon for nothing. Wake up.