Mine would be similar, but I am 6'3", weigh 255 and live at 5300ft elevation. It was worse before I reworked the airfilter and airbox. The X500 does not have a very wide range CVT which I expect is due to the same engine/CVT being used in the Kymco 500cc ATVs (with a few changes I suspect).
We also have a 2005 Burgman 400 (385cc actual) and it's CVT is much more responsive with a better range. The Burgie will also beat the X500 in a drag race up to about 40mph. Where the X500 shines is the tractor like grunt from the engine which pulls well here in the mountains.