Actually, I have an entirely different take on what it takes to have a horse that enjoys his job and enjoys obeying a fair and competent trainer / rider / leader.
I think most horses crave structure and knowing exactly where they stand in the 'pecking order'. I have observed horse behavior for 55 years and have taught them what I wanted them to know for 50 of it. I have found that the horses that have been taught a very solid structure for their behavior are the 'happiest', least stressed horses I have been around. They become so willing, their ears are up and alert, they listen and patiently wait for each directive. They are not unsettled or mad or worried or defiant about anything. They just go on doing what is asked of them for years.
They are not 'beaten down' or droopy or unhappy. They nicker every time they see their human herd leader and come to depend totally on their 'people'. When I step out in the pasture with an armload of halters, it is more like each horse is saying "Take me!" "No! Take Me!" they each patiently wait for their turn at getting a halter on. I frequently lead 6 or 7 geldings out of the pasture together. Sometime when I am in a hurry, I lead 2 out the window of the chore truck and husband leads 5 or 6 more off the back of the truck -- usually at a good trot. Don't anyone tell me they would rather have it any other way. Just like a foal does not question where its mother is going but just follows because its dam is its leader, a well trained horse does anything its leader / person wants it to do and does it happily. It not only likes the structure of knowing who its leader is, it requires such a relationship to be happy and well-adjusted. It is just the way horses are. All of my years of observing feral herds, ranch herds numbering in the dozens, family groups, stallion led herds and mare or gelding led herds. [They really differ little except during the breeding season when the stallions are functioning as stallions.] Oddly enough, you can turn a group of stallions in together in the fall when the breeding herds are brought in on large ranches and even a herd of stallions behaves just like any other structured herd.
If you want to see an 'unhappy herd' where everything and everyone is upset and unsettled, just scramble up the make-up of an established herd and switch horses around. I did it this year when the ponds and creek started going dry. I had horses run over fences, I had horses kicked and bitten all over and had one that we are still doctoring and may be crippled. They had a very settled structured herd and absolutely no problems. All were happy with their place in their herd from the most dominant down to the ones at the bottom of the pecking order. Moving them around completely destroyed their happy settled herd life.
Horses are terribly unsettled and unhappy when they do not know where they stand in a herd -- be it a horse herd or their human herd. They are mean and fight for the best place they can get into in that pecking order. Once it is settled, they accept their place and are very happy. Oddly enough, those at the very bottom of the pecking order are the happiest. Those jockeying for a better position near the top are the most unsettled.
I have found that when horses are at the very bottom of your pecking order with them, they are also happiest. They never show resistance or aggression. They are more like the yearling or foal that 'clacks' their mouth to tell you that they are not challenging you. They want you to know that they look up to you as their leader. They would not even think of being pushy or biting or kicking.
This is the kind of relationship I have with every horse I handle. They are happy letting me be the leader. They do not have an opinion that I want to know about.
When I see people struggling with a pushy horse, I see a herd that has not established the pecking order. I see horses that are mad and aggressive trying to convince their person that they are the herd leader. Don't try to tell me that a horse that is trying to become the herd leader is a happy horse. Don't try to tell me that a horse that a person is listening to is happier than a horse that KNOWS its person calls all of the shots. I have watched too many horse herds and people / horse herds to know that that is just not how a herd animal thinks. When they have accepted a person as the herd leader, they are happiest. If they are pushy, if they are laying their ears back at a person, if they nip or kick at a person, if they defiantly refuse to lead or back up or move over, they ARE NOT happy in their place. They are fighting for the leadership role and are pretty unhappy and miserable acting out. Like the unhappy spoiled, tantrum throwing brat that defies his/her parents, the 'spoiled' defiant horse is miserable. I have seen it over and over and no one is every going to convince me that a horse is happier that has a bossy leader one minute and one that wants the horse's input the next. Horses want structure and to know where they stand and they want that place to be the same every minute of every day.
Congratulations if you waded through all of this!