Every arranger that comes out has basically the same ratio of old and new. And it is all usually no more than 10%. How many NEW sounds and styles did the T4 get, compared to the total number of sounds?

About the same.

If you like Yamaha, you aren't going to change ships for a mere 10% new in a Korg. And vice versa.
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An arranger is just a tool. What matters is what you build with it..!