Fair enough and doing a search it appears that the GNS/XLS is counted as a FMS these days and is also PRNAV (with a software upgrade). I have a reasonable bit of time on them.
I always took FMS to be able to do VNAV and link into the vertical modes of your AP.
Well you live and learn. Any box of tricks that can do LNAV and drive your flight director is now a FMS.