It's very easy to screw up the controller when designing a device. And if the built-in controller sucks, then it's completely worthless no matter how powerful

It's very easy to screw up the controller when designing a device. And if the built-in controller sucks, then it's completely worthless no matter how powerful it is. D-Pads especially are hard to get right. You can either be way too lenient on diagonals, or way too hard to hit diagonals. I had a Chinese handheld where you couldn't consistently hit Down while holding Right. Sonic runs into the enemy because his roll attack didn't start.