Complex sentence: The result was still not good enough although it came close to its rival Bf-109F in performance and was superior in maneuverability, as even with the lighter airframe and supercharged engine, the LaGG-3 was underpowered and proved immensely unpopular with pilots.
Split into simpler sentences: The result was still not good enough although it came close to its rival Bf-109F in performance and was superior in maneuverability. Still, even with the lighter airframe and supercharged engine, the LaGG-3 was underpowered and proved immensely unpopular with pilots.