I dont believe in the whole 'your the boss' thing. I mean you have to be up to a point but if you can make both happy then why not?
But you see the whole thing about horse training is NOT what you believe, but what the horse understands and believes, and they simply do not think like humans.
Horses want a boss, or they want to be boss, there is not a lot in between, and to try and make that, can lead to a very sour and frustrated horse. A horse equates a 'boss' or more properly 'a leader' and in all worlds there is a clear difference between the two, as security and safety. A leader will look after him, and protect him, all the horse has to do is stay respectful, and obey the rules.
If there is no one strong enough to lead, to be that protector, then he thinks that he has to step up and be the leader, so now he thinks that you should do as he says, and will keep trying to assert his authority. That is a rotten thing to do to a horse, so be a decent person, step up and be the leader than he needs, and by doing that give him comfort and security, because he knows a leader will protect him