What you're talking about has nothing do with what transmission the tractor has but rather how the load you're pulling is attached to the tractor. If it's attached above the center line of the axle, bad things will happen.
It depends on the use. If the main use is mowing/brush cutting, extra weight just wases fuel moving the tractor around. But for heavy pulling and FEL work, weight is quite important. That is why I chose the Mahindra over the Kubota, though I have had a Kubota in the past. But the Mahindra weighs in about 1500# more than the comparable power Kubota model. It also has larger tires, more 3-point lift capacity, more FEL capacity and larger axles. If I were doing lighter work, I may have preferred the Kubota.
Actually it does have to do with the transmission. If you have a gear drive, it will not stop unless you push in the clutch. This requires fast action and coordination. With an HST, if your foot goes off the HST pedal, which it will do when you start to flip or rollover, it will stop. So it requires less operator skill. Also, a tractor can flip to the side when it hits a hidden obkject. I have had this happen when underbrush hid an old stump. As far as drawbar location, what you say is true. But when logging, you want to get the log off the ground to avoid plowing a trough all the way back to the landing and getting the log all muddy. The act of lifting the log will put more of the load on the top link. Have you ever seen how high up the winch point is with a log skidder? Some are 8 feet off the ground. But most of the weight is up front. I mimic that weight distribution by having a heavy FEL.
I used a 1974 Ford 4010, I think. It was about 53 Hp, as I recall, and dry weight a bit over 5000#. It had a 3-speed trans and a high and low range. Low range was pretty slow in 1st gear. We added wheel weights to the front, so it was pretty stable. But it was a 2WD tractor, so it was not that great in the woods anyway. In though areas, I used a Kubota B7100HST. But it was smaller than what I really needed. Good little tractor, though. I managed to completely wear it out after about 20 years and 2600 hours. I ran a 4' Bushhog, an FEL, a 60" finishing mower, a 50" rototiller and a 4' scraper blade with it. Those implements were pretty much all it could handle.
If I'm doing any heavy pulling, the foot will be close to the clutch, ready to press in case something goes bad. Plus, I'm running on the slowest gear I have and the throttle won't go above 1500RPM because it really doesn't need more than that on such a low gear. Plenty of time to react if anything go bad.
You are missing the point. Kubota is historically known for lighter machines in a given “class” if you look at dimensions of the machines. Thats what I am saying.
I guarantee, if you hit an unseen obstacle in the woods, even at low speed, your foot would jerk away from the clutch pedal. And if the tractor really did start to do a wheelie, at 1 mph with a 50" tire, it would take about 2s to reach 90 degrees, the point of no return. My bet is you would have trouble keeping your foot on the clutch then, too. Of course, you could put anti-rollback legs on the tractor, as they do in tractor pull events. You could also pull with a scraper blade. Any large implement would stop a wheelie rollover, but not a side rollover. And I still had a close call with a sapling that popped up when it hit the front axle and ran into my chest. It nearly broke my ribs, which hurt for a week. And this was with an HST, where all I had to do was stop pressing the pedal. I am not trying to say which transmission is "better". I am trying to point out situations where there is an actual safety difference. And any system which requires more operator skill to avoid an accident is intrinsically more dangerous. I think that should be obvious. And the original poster indicated a variety os uses for the tractor. Woods use was one of them. That is probably the most dangerous activity a tractor can be used for,