The truth is no archetype is needed, except during Hamidon. Technically most archetypes can do what another archetype does, for the most part, without needing the other. A really decked out blaster doesn't need a tank or brute because they murder everything too fast, same for a scrapper. A lot of people will argue defenders aren't needed at level 50 because fully IO'd people don't generally need a lot of help. Honestly, it's best to not look at City of Heroes with the 'Holy Trinity' of tank/heal/DPS in mind.