The horse mechanic where it slows down if your mouse is close to it is driving me insane.

Absolutely.

I want to race around Sanctuary like my horse was powered by fire of Diablo itself, instead every time I try to turn my horse has to slow down, and take a moment to inspect some random demon's armpit.

Force Move should be 100% speed when mounted

I don't hate this as much as I used to now that I've found a reason to go slow on the horse - PVP. You sit on your horse to get a larger field of view and trot around, you don't want to spur the horse because other players can hear that. Now this is literally the only time I can think of where its advantageous to idle on the horse, and move around slowly, but its something.

I think generally speaking they've got to know that the horse just isn't very fun. Getting stuck constantly, checking the map constantly. Needs a lot more polish.

My wife and I didn't even realize this mechanic for a while and were confused why our horses would go at different speeds all the time. We figured it out eventually, but the mechanic is unintuitive and not at all user-friendly. I looked through settings hoping to find some sort of radius setting to reduce the mouse drag distance and was disappointed to not find anything.

Yeah, its a bunch of issues that compound to make the horse kind of a pain in the ass to use:

1. 3 tier horse stamina mechanic is dumb.
2. Toolbar HUD is way too big on certain screens and there's no way to configure it, which means it interferes with horse travel and teleportation. Only thing you can do is move the toolbar to the left corner, which sorta helps.
3. Bumping into a wall or barricade doesn't stop the drainage of horse stamina.

What I really want is:

1. One long stamina bar that drains at different rates depending on the horse's speed.
2. Have the horse speed mouse diameter be between the top of the screen and the top of the toolbar.
3. Horse stamina stops draining when it runs into a wall.