I wear a size 12 boot, so spanning forward/rev is not a problem and I can rock my foot easily. I think a size 10 is about the minimum requirement to easily span, as supported when my brother uses the tractor. Neither of us has a problem smoothly changing direction. My wife has a smaller foot and has a little more difficulty, but has learned to do so pretty well.
It is indeed a learned skill. I am sure you have read complaints about the RTV "abrupt stops", but my wife and my 9 year old grand daughter drive the unmodified RTV1100 with absolutely no difficulty in smoothly slowing, stopping, or changing ranges. Yes, one could get thrown into the windshield by immediately taking your foot completely off the throttle, but you could do the same by stomping the brake in your car/truck, and you probably don't. ...a practiced, learned skill.
As far as when I use the clutch, it is to start the tractor, to engage the PTO and sometimes to change ranges. The old B only has two ranges and doesn't always cooperate in range change without the clutch. Because it only has two ranges, I use it in H as much as possible and often already have it under a load when H proves not quite up to the task, so it is easier and faster to dump the clutch and change. Most other times, when I know I need L or H prior to having its ears pulled back (LOL) I can shift without the clutch. I can make any other move with forward/reverse pedal...and move millimeters if I chose to do so. (I also brake steer using my left foot ...size 12 boot.)
I hope that helps with your questions.