Based on everything that has been released, Overwatch 2 will play differently from the first game. One of the changes sure to have a huge impact on the gameplay is the reduction in the number of players on each team in player-vs-player matches. Teams will have five players each in Overwatch 2 compared to the 6-v-6 gameplay of the original.
Such a huge change can affect every aspect of the game and by extension can raise or lower a character's effectiveness. Overwatch's Community Manager AndyB has been discussing these effects on the Blizzard forums. Specifically, AndyB spoke about how they might require a change to Zenyatta's discord orb and Mercy's damage boost.
Zenyatta's discord orb may be the ability affected the most by the change to 5-v-5 because there would be one less teammate who could deal damage to a debuffed enemy. Mercy's damage boost ability only buffs one ally at any given moment, meaning she may be somewhat unaffected by the change to 5-v-5 gameplay.
In any case, Blizzard seems to be listening to the community and willing to make changes to characters as development continues.
"Thus far in our playtests, Mercy's Damage Boost hasn't shown any major issues," AnyB said. "That said, there's still a chance we end up tuning both Discord and Damage Boost down, if we see they're causing issues in further testing."