Original sentence: MDC had seen off stiff competition from Lockheed in the '70s (Lockheed withdraw from civil aircraft manufacturing after relatively lacklustre sales of the Tristar), but even with new, fuel-efficient engines and many changes, the MD-90s in the 150 seat class were unable to compete successfully with the similarly sized Airbus A320 and 737
Edited sentence: MDC had seen off stiff competition from Lockheed in the '70s (Lockheed withdraw from civil aircraft manufacturing after the failure of the Tristar), but even with new, fuel-efficient engines and many changes, the MD-90s in the 150 seat class were unable to compete successfully with the similarly sized Airbus A320 and 737