They aren't as similar as they seem at first sight. The main CPU in Black Tiger is twice as fast, and it has a second one. Several times the working memory. Several times the ROM size of a Master System game. Much more powerful VDP capable of more sprites and better sprite manipulation. Far superior sound hardware. Far more video RAM.
Black Tiger is closer to the Genesis or the Turbografx than the Master System. The Z-80 does not tell the whole story.