I'm pretty sure the gamegear lost that war because it couldn't really be used as a handheld. Not with that battery life.
The game boy may have been a very limited system, but you could bring it with you and play Tetris for hours and hours... or for its second wind, show your pokémon to everyone at school.
I remember reading about how mind-blowing and "next gen" the graphics on the Dreamcast were at the time. All the kids seemed really interested in it, but we hadn't had long enough with the previous gen to justify our parents buying a new system already.
One friend wound up actually getting it, and we played the hell out of it for a few years.
The Game Gear was only good for 2-3 hours on six AA batteries, so you basically had to play tethered to the wall or invest in lots of rechargeable batteries. The library also wasn't as strong overall as the Game Boy's, although its top games were previous-gen console quality (because they literally were in other territories).
Both screens were also just awful about blurring during fast movement. Nintendo wisely avoided it altogether, while Sega was bound by their flagship brand. When you really got going in something like Sonic Chaos, particularly considering the small viewing window, you were really just letting Jesus take the wheel.
Both screens were also just awful about blurring during fast movement. Nintendo wisely avoided it altogether,
While mostly true, they should have told Rare too. Between blurring and bad contrast, Donkey Kong Land was almost unplayable.
(By the way, screens with bad blurring from fast moving stuff were still a thing for a long time after that. Dracula X Chronicles for PSP had the original PC-Engine Rondo of Blood in it. Small, fast black bats on a bright background were almost perfectly invisible)