Lee, many of these statements are just wrong. For example, there is a parameter to set the tempo to remain constant when switching styles. There is a one-key chord system, although it is proprietary.
You can play your own intros, endings; just start the style and play them! Play an ending and then hit simple ending one.
The fill system works well. The variation buttons all have their own dedicated fill patterns. If you press the variation you're on, it fills to self. If you press another variation button, it fills to that variation. You can also use intros and endings as fills.
Press exit button to return to main screen. If there are several screens active, press it several times. I can press it 3 times in about 1/2 second.
The T4 harmonizer is much improved and I hated the old one, but it was usable with some editing and setup precautions.
I don't have plans to get another Yamaha right away, but they do have many insightful features in the OS.
Regards,
DonM