I will relate an experience I had. While bushhogging in the woods with a Kubota tractor with an HST drive, I mowed down some saplings perhaps 2" diameter. But some of them did not get cut through; they just got pushed down under the tractor and bushhog. When I retuned going back the opposite direction, one of the saplings had started to rise back up, and it was slightly higher than the front axle of my tractor. When I drove back over it, it popped up and hit me square in the chest, going between the tractor body and the loader frame. I had a sever bruise and it hurt when I breathed for days. It probably came close to cracking my ribs. But if I were driving a gear drive tractor, it probably would have run me through, as all I had to do to stop the tractor was release the pressure on the foot pedal, which is much easier to do than to find the clutch on a gear drive tractor and push it in. I also have experience with a couple of gear drive tractors, and I usually did not use the foot accelerator to control speed; I used the hand throttle. I guess using the foot accelerator would be safer in the woods, but not as safe as a hydrostat.
I've been a commercial mower, using tractors since 1982. I have never gotten into a situation like that, but that was probably because I had a bit more expertise about mowing brush. I can see how it might happen. It sounds unpleasant.
You should also be aware that the brush going the wrong way under your tractor is far more likely to get caught up in your foot lever linkage and strip you of any ability to control the tractor hydraulics. I don't consider that hydrostat is superior to clutches, at least with respect to operator controls. That depends more on the skill of the operator than which foot pedals he must engage.
Over the past 40+ years, I've seen lots of my guys lose control of the machine. I've had them upside down, high centered, axled into the mud, fallen off trailers, down into ravines, and many times I've had the operator stop the tractor and walk away from a dangerous position, saying that I would have to come drive it out.
I think hydrostats are superior to clutches in many situations, and certainly for fellows with less experience. I generally prefer a clutch with a shuttle-shift for rapid forward and backwards maneuvers. A clutch and geared transmission will outlast a hydrostatic machine by many years, and at lower operating cost. Hydrostat machines are much better at working the machine hard under load while doing tight maneuvering. Grading, back & forth loading, perhaps running an attachment like a post-hole digger are much easier with a hydrostat machine. Field mowing, towing big loads or driving down the road at high speed are much less work for a gear-drive machine.
I think if I wanted a small utility tractor for working in the woods, I'd prefer a hydrostat, too, unless my budget dictated that I was keeping the machine for 20+ years. Then it's clutch and gear drive only.