Keep in mind that the Genesis came out several years before the SNES. It was designed to compete with the NES.

If you compare the NES and Genesis, the Genesis looks pretty great. It doesn't have quite as many classic games, but the game design is more modern and it blows the NES out of the water in terms of raw power.

Considering people pit even more emphasis on power and specs back then than they do now, I can't imagine many people regretted having a Genesis instead of a NES.

Now once the SNES came out, that's when it became a real battle... and everything after the Genesis was a pretty big flop commercially (except the Dreamcast) so very few people had them instead of a Nintendo/Sony console.

The Game Gear is cool but it has very few original games. Almost all the games in it's library are just conversions of Sega's 8-bit home console games. In Sega's strongest market at the time (Europe) that meant most people already owned all the big games for their home console. It also has a blurry screen and eats 6 AAA batteries in about 3 hours, which is just unacceptable. It was also much more expensive than the Game Boy.

It actually sold very well for a while, but third-party support was dreadful so most people moved over to the Game Boy which had more games and cost less.

I think most Game Gear owners just left it plugged in and used it as a handheld TV after a while, since you could buy a TV antenna for it. I love the console but the technology just wasn't advanced enough to achieve Sega's vision for the device and there was basically no third-party support. As Nintendo has seen, good exclusives and cool technology aren't enough to keep a console alive.