Complex sentence: Many of the video game systems were technically superior to the Atari 2600, and marketed as improvements over the Atari 2600, but Atari dominated the console market in the early 1980s.
Split into simpler sentences: Many of the video game systems were technically superior to the Atari 2600, and marketed as improvements over the Atari 2600. However, Atari dominated the console market in the early 1980s.