In addition to what UD said, these workstations (non-arrangers) have exstesive features for modifying and building sounds. In other words, they are synths. So if you are the kind of person who loves to stay days tweequing sounds to get certain sci-fi feel, welcome to the synth world. The only professional arranger that has this capability, IMHO, is Genesys.

Furthermore, the real value in motif es is the fact that it contains the largest library of sounds.

I have always questioned why Yamaha cannot produce another keyboard that is motif-es, but has the styles and harmonizer of tyros: Motif-es-arranger.