Agreed Ian.....you definitely need an arrager KB that is Capable to perform in the manner and style of Tyros 4 in the first place.... playing ability comes in second.
Donny, I also believe playing ability can make a big difference, especially if the performer can play many genres of music with basically equal skill.
Some players are more at home in certain genres, but, the
arranger itself should be capable of covering
most, if not all, types of music, equally well.