It's completely different in 3v3 vs 6v6. In fact 6v6, it's without a doubt OP (Sunbreaker is all I use in PvP anymore). In a round based game mode like Trials where there also only happen to be 3 enemies it's not very effective. Everyone has their super around the same time to counter each other, and your out of super abilities play a larger part than your super (not that the Sunbreaker's non-super is bad, it's just not as good as some others). You also tend to have a lot more coordination amongst your team in 3v3 than 6v6 to attempt to counter them (unless you only PvP in a fireteam).