BlueSpark, I can totally agree with what you write, a horse should be a horse and treated as such, they don't make good pet dogs. It felt like you were directly relating to my post (since you quoted me), I'm glad you clarified.
It's great you never even have this problem. I had horses that were slightly "barn sour", but mostly they were just nervous about being taken from a safe place into a world full of potentially dangerous things and creatures, without their horse buddies. I wouldn't call this a problem, either, but I just prefer to ease them into being out with me by walking them. It's just part of their groundwork (actually, it's most of their groundwork), and sometimes I walk them instead of riding just because I feel like it, they enjoy it, and you can do fun, trust-building stuff like jumping ditches together... they all relax when it becomes a routine to be with just that human to rely on.
I'm sure you can be a great leader for your horse in the arena and if they trust you enough, they will do anything, no matter how scary. But that doesn't work for everybody. I don't think most people have it in them to be such a natural leader, and if the thread starter had it in her, she wouldn't have this problem with her horse. Making it a routine to be out on the trail walking together might be an easier and more practical way for her to get her horse's trust than asking her to just be a better leader in the arena. From what she wrote, it doesn't sound like the horse is downright panicky or dangerous to handle away from the barn, so her plan including walking and treats is a realistic option. I would put a rope halter on him, though, for better control, should he start acting up more. I'd also take a carrot stick or whatever you use for groundwork to be able to set boundaries better.