Chas, most of what you say is true, but I believe Gary is on the money...arranger keyboards are more versatile...
They combine a lot of different ways to perform with a single keyboard..

I use the Roland G70 as a realtime..bass piano/organ and drums combo ..more so than full arranger modes..The only automatic play being drums as any other drum machine..I have the options of adding "color" sounds to my main sound , such as piano...

The versatility continues with mic inputs, harmoniser, and effects..

The versatility also continues with SMF playback..

The versatility also includes all mixing capabilities..

So where do you find Gary to be wrong with his statement?