It depends on the situation.
Voidwalker warlock with attunement of hunger can basically always regen health, which makes it very effective at staying alive in PvE - but this doesn't help in PvP at all.
Apart from that, I think you need exotics to make any of the other classes really stand out - like striker titan wearing Insurmountable Skullfort (every melee attack is a special), or gunslinger hunter with Celestial Nighthawk (super is a single shot that does a ridiculous amount of damage).
But Steven is right, nothing is op in destiny 2