The arranger keyboard is a pre-set instrument, as an example the Tyros SA Guitar, everything is built in to make it sound good even if played by an inexperienced player, however unless one of the on-board guitars matches what is required in a production or band setting, they are of no use.

With a workstation you get basic guitar sounds, which you then add the embellishments you want, (Using real time controls) for your production or band play and save it in a patch.

To setup the guitar on the arranger, you have to remove all the manufacture applied embellishments then add what you want, however because an arranger has severely limited real time controls and limited editing features, (You have to keep switching between menus which is time consuming) means making a setup for your specific use a pain in the rear. (Yes it can be done, but no one in a production or band environment wants all that hassle)

Bill