I had a 7800... I doubt it would have done as well as the NES even if it had the market to itself. It was a step up from the 2600 to be sure, but the joysticks left a bit to be desired. The general complexity of the games released for the system was lower than those for the NES, which is good and bad, but the system never had its "Wow" moment - outside of a relatively decent game of Pole Position II. The Master System might have done rather well were there no NES. In fact, I understand it did quite well in Europe. Despite a few technical advantages for Sega's system however, it was the software released for the console that really brought things forward. That's where the NES truly had the advantage. Sure, the Master System had Phantasy Star and Alex Kidd, and a better version of the original Double Dragon, but the Mario, Zelda, and myriad third party properties helped bring the NES to the forefront. Super Mario Brothers in and of itself was IMO the key property - a killer app, if we're into overused terms - that allowed it to own the market. The game had simply spot on controls, like nothing else at the time.