They die from heat, not mileage
M274/M271 engines run very hot - coils sit directly on top of spark plugs inside the engine cover. Heat kills the epoxy inside. That's why Benz coils fail earlier in Ghana heat than in Europe.
2. One bad coil = put car in limp mode
Mercedes ECU is very sensitive. Even one misfire (P0301-P0304), it will cut power, show "Check Engine", and limit speed to protect catalytic converter.