Zarya doesn't really have the damage soaking of a main tank or the DPS of a DPS hero. At full energy her beam sits just below 200 DPS which seems huge until you realize she can't headshot. What she really brings to the team is CC/burst immunity and Graviton. Barrier can be clutch in saving yourself and your teammates but you end up not doing much if your cooldowns are baited out. Graviton's a great ult but you shouldn't expect to build more than 3, realistically 2 of them in a single round and if it gets eaten by Defense Matrix or deflected by Genji then the last 2-3 minutes playing Zarya was effectively wasted. High level Zarya vs D.Va is a game of waiting for the de-mech before you even think about Gravving which can be difficult to accomplish if the D.Va is respecting your beam range.