Sega’s only console success was Mega Drive/Genesis. Probably because “Sega does what Nintendon’t”. Sega managed to sell themselves as the alternative for the kids who were too cool for the SNES.
They couldn’t compete with Sony on that front. Sony was the new cool guy. Dreamcast failed because everybody was waiting for PS2.
So I’d say failed marketing killed Dreamcast.
The numbers I can find of Master System is that it sold between 10 to 13 million units worldwide, so not that much better compared to the short lifespan of Dreamcast.
Mega Drive’s sales numbers isn’t too far off from SNES.