Actually, a guitar is a mono instrument! Unless you are listening to it VERY close up, all sound appears to come from a single point.
If you are hearing spatializing differences (I was trying to listen to the guitar, silly me!) then that comes down to the choice of reverb used, and the depth of that reverb... which may be something that can easily be changed on the Yamaha.
Add to that you get considerable control over mastering EQ's and compression, and, unless all of this is taken off both arrangers (and the guitar recorded dry) you really aren't comparing apples to apples.
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An arranger is just a tool. What matters is what you build with it..!