Sampling has always been more an art than a science. Bitrate doesn't make up for poor samples in the first place. Yamaha actually make real saxes, pianos and guitars. Perhaps that's what gives them the edge? People in house to go 'that's not quite right, do it again' because they KNOW what the instrument should sound like...
Yamaha, to give them credit, have always done a superb job of pre-EQ'ing their samples so they all blend together pretty well. While Korg tend to go for a sound that is full, and it's up to YOU to EQ it to match whatever style you are using. A bit more flexibility, a bit more work.
And also, let's give Yamaha the kudos for being the first hardware arranger (actually, I think the first hardware keyboard of any kind) to do legato and staccato articulations, and conditional sample switching (slides when you play over a certain interval, for instance), all of which were VSTi only features up until the Tyros line.
I'm afraid that, although Korg have jumped onboard with their DNC capabilities, they still haven't quite got the sound set and samples to leverage it as well as Yamaha have. But that's just a matter of time...
BTW, huge kudos to Korg for the ribbon... There is some stuff (trills, hammer-on/offs, fingered vibrato etc.) that cannot be done with a wheel or lever. Wish more arrangers had those!
An arranger is just a tool. What matters is what you build with it..!