If there were no lacking features in the PSR 9000 then there should never have been a T1, T2, T3, and T4.
Yamaha thinks different from you in that they do not think a lot of persons are using their older arranger. If they did they would not be making so many new arrangers.
Look Ian you may not agree with Yamaha’s way of business but that is what has been working for them and other manufacturers should follow if they want to stay in the TOTL arranger business.
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TTG