No such thing as a Hustler X-ONE with a Kawasaki FS unless someone replaced the FX with an FS.
Not sure what you mean by "bulkier". Usually bulky has a negative connotation when referring to mowers.
Not sure what you mean that "taller" is better when comparing mowers.
I've had an X-ONE, 60" rear discharge, FX730V Kawasaki since 2012. It is used in a 200 year old cemetery, it is one tough machine that is easy to service and at 1,250 LBS is smooth riding.
Current X-ONE models now have an adjustable suspension seat, but I don't feel the need for one as the seat on my 2012 machine is very comfortable.
I did replace the stock seat on my Scag Tiger Cub with a suspension seat.
Were I in the market for a new machine, I would consider an engine with EFI.
When looking at prices, one must compare apples to apples. EFI engines are more expensive than carb engines.