The Kubota I owned was a gas 500....when I'm saying the diesel doesnt' have the grunt I'm going off the test drive only and comparing the JD gas/diesel options. When I test drove the RTV diesel it had the same lack of suspension travel and lousy hill climbing acceleration the 500 had so Kubota was ruled out quickly. I'm also not a huge fan of the let of the go pedal and get lurched forward feel the 900 I test drove had.
I think there's a reason all the snow groomers that use side by sides, power companies, and road crews are using Gators/Rangers and not the Kubotas...a lot of people claim that the CVT transmissions can't do any work but that's proven wrong on a daily basis. The Kubotas have a following but it's mainly in the residential side and then it's typically from people who use it on a relatively small property only....for recreational use they aren't close to the competition.
Locally, I see a ton of Kubotas in use in construction and logging. Deeres mostly in landscaping, golf courses, property management, commercial real estate, etc.
I don't know about the older Deere and Kubota models, but when I was shopping at the end of 2015, it was no contest -- the new RTV-X diesel models (900, 1100, 1120) were significantly better than the Deeres in my experience. I am told they addressed a lot of the issues on the older RTV 500/900 models, but I never looked at those, so I can't say personally.
I like/shop/own both brands, so either Deere or Kubota would have been fine, but the RTV-X1120D popped to the top of the list with some big advantages, including build quality/construction, power/torque, suspension, and the transmission. There is really no comparison between the CVT and the HST, it's night and day difference.
Again, I don't know how the older models compared, but the newer RTV-X models are clear "working class" UTV leaders in my mind. The only disadvantage they have due to diesel/HST is top speed. But my RTV-X1120D hits 28 mph and that is plenty for my uses. I rarely get to go that fast except when traveling large distances on trails.