Diki said: “yes, it needs a well integrated sound set (or patch selection live is a nightmare), yes, it needs an easy to operate OS (or your live show is a nightmare.”
I am sure we can agree that these two requirements are subjective. Not that they are bad to have on an arranger (or any keyboard for that matter), but what may be easy to you may be hard from me. What may sound good to me may not sound good to you.
Yes you are correct that an “Arranger” is an amalgam of components. The question is what is the minimum requirements for “amalgam of components” a keyboard must have to be called an arranger.