It's not about the power output of the engines, it's purely about their size and the way their aerodynamics affect the aircraft at high angles of attack. Airflow upwards from below the aircraft push the engine cowlings upwards. On the old design the main part of the engines was close to the center of mass and didn't affect the pitch of the aircraft. The new engines are both larger and further forward. At high angles of attack the airflow from below pushes on the engines and because they are so far forward this pushes the nose of the aircraft up, increasing pitching moment. To counter this the MCAS system was introduced that counters this extra pitch up moment by applying nose down trim such that the pilot wouldn't feel the difference. However, when the Angle of Attack sensor fails, the MCAS system repeatedly adds nose down trim when not needed, until the pilots have to pull on the yokes with 50 kgs of force just to keep the nose from dropping. On 2 flights they lost that battle and the aircraft dove into the ground.