I think he's referring to soldier's:
- Sprint, making his reposition faster than most other DPS
- Hitscan damage, which is reliable at short and medium range and can still help at long range
- Self sustain + ability to heal his team
- Burst potential with rockets
Soldier can shoot at long range enemies and hit them reliably, then whip around and kill Tracer with a rocket and 1 headshot, then sprint up to high ground and aimbot the enemy team, and it's all point and click. Reliable