This is just another case of gathering information from all sorts of sources and evaluating it to see what might be useful.
A herd actually does need a passive leader that will have the calm courage to lead wherever they need to go, keep the others settled and at ease. Horses in the wild couldnt afford to waste an ounce of energy racing off every time a twig snapped or a bird farted. A wise mare knows when theres real danger - horses have amazing powers of scent and will pick up the smell of a predator before its a risk to them. The lead mare then wants the others to follow her away from that danger and to safety - not to be running away from her like headless chickens in all directions because they don't trust her to not be wanting to attack them for some reason
An aggressive handler usually makes a horse tense and nervous even though it might appear to be compliant.
Do not confuse passive with stupid and dull.
This passes on to your horse in the way you ride it. It sees something it finds scarey but if it trusts in you and you stay calm then they will believe you. I rarely need to desensitise my horses to anything more than the general way of them getting used to stuff around the place because they see me as someone to trust and not someone to fear.
Understanding horses and their behaviour doesnt mean we should become like horses ourselves. We learn their 'language' and also educate them in ours They have the approximate mental ability of a 2 year old child, as adult humans we are far superior to that.
Early man could never have captured horses and domesticated them on their terms - they are far faster and much stronger than we are.