I can only speak from my own experience. I'm not a pro. I'm terrible at two-handed piano. I don't think i have particularly good finger articulation of my left hand, either. So when I play arranger, it's strictly left-hand chords, right hand melody. Playing fewer notes reduces the frequency of having to reposition my whole hand to reach all notes of the chord, which facilitates rapid chord changes. In my case, I think that pressing fewer keys also reduces the number of errors. If I had to play all the notes of every chord, I don't think I would be able to make keyboard music at all!

On Korgs I use the system called "Fingered" with the split active. This allows me to get a major chord with only ONE note left of the split point. Minors, 7ths, Major 7ths, suspended 4ths, augmented, and 6th chords are all achievable with just two notes. 9ths and some other tension chords can be played with 3 notes. The Korg system is great if you don't play a lot of "on bass" chords. If you do, I find that some of its two-finger shortcuts "get in the way." [When you try to play common slash chords like C/G and C/E they are recognized as Gsus4 and Eaug respectively. This COULD be fixed by a menu option, but to my knowledge it has not been.] After testing all the brands, I've found Roland's Chord Intelligence most to my liking, followed by GEM and some recent Casio products. But GEM is defunct and Casio's quality is not up to par. If Roland stops selling arrangers it will be a big loss!

The best systems on the SX900 are "multifinger" and "AI fingered." Neither one is to my liking. For minor and 7th chords, multifinger sometimes requires you to play notes which weren't part of the original chord. [Thus by extension, some progressions might actually be MORE difficult to play! By comparison Roland, Korg, GEM strictly use a SUBSET of the original chord, so it's always easier than the original score.] The AI Fingered mode is Yamaha's attempt to facilitate playing slash chords. Many two-note fingerings are recognized as an "on bass" chord. Unfortunately IMO, for majors and other chords you need to play a minimum of TWO notes, and more often three notes. So not as convenient as Korg, and not nearly as good as Roland, GEM, or Casio.