Defender is a support and provides a place of sanctuary from the enemies and gives people a shelter to regen health. Striker is an offensive class that has zoning capabilities and a high damage with a good radius that destroys mobs (more PvP.) Sunbreaker is a generally weaker class unless they have their super. The sunbreaker is a very high damage roaming super that is super focused and not any passive abilities. The problem with an all support team is that there is no offensive abilities. A fireteam needs to cover all bases, offensive, defensive, support. A team doesn't focus on all one element, a team comprises of people all specialised in different focuses.