I'm not sure whether it's unfamiliarity with English, again, Frans, but 'It's a proven fact' is NOT an opinion. It's a declaration of FACT, and has nothing whatsoever to do with opinion.

In actual fact, the only way you can PROVE something about an opinion about sound is to provide example for your opinions, and get the majority to agree with you.

If you think that Korg (or any keyboard) is 'better' than any other, provide your example playing it, and see what people think. And even then, don't expect many to agree with you...