A couple of points:
The kubota (or Deere, Yanmar, Cat, Ford, etc) engine is designed to deliver it's hp all day long. Very few gas engines are designed to do this. As an analogy, the chevy 454 or ford 460 will run circles arround a diesel (more torque, more power, more speed), but people who are serious about towing will go with the diesel. It won't wear out from delivering it's rated load. OTOH, if you buy a 200 hp diesel, just to deliver that burst of power when you need it you are wasting your money.
Diesels will typically burn half the fuel of a gas engine at rated load- I'm not sure if this still holds at the low end of the size range we are discussing. In an over the road vehicle, the weight of the diesel will hurt fuel economy, in a tractor it's an asset.
Compairing a hyped up lawnmower to a toy size tractor isn't a fair compairson. A gas ford 1000 or 8N would be a better reference point.
When compairing tractor horse power, you have to look at how it was tested- PTO dynos are a bit hard to cheat, assuming it is run at rated PTO speed. Drawbar hp is meaningless unless a standard such as the nebraska tractor test is used. Engine hp number are a bit meaningless and easy to cheat with. Gasoline engine hp is generally 50% higher then an electric motor for the same load (assuming it was designed by a engineer.)
If you want to talk about pulling power, I used to operate a tractor that would pull any ag tractor under 100 hp backward- It was a 20 hp case stream traction engine. A steam engine will deliver max torque at 0 rpm. A large (say 80 hp) HST might move it, but I don't think such a critter exists. Then there is the traction factor, your HST has 60 lbs of diesel, mine had 4000 lbs of water, and 100 lbs of coal. Your body might be 14 ga steel, mine was 3/8" steel plate.
Pat