If my pipes break tomorrow I call him and he takes care of it. Someone comes and fixes it that day or the next.

Right, he paid for that plumber with money from your rent in excess of the cost of the mortgage. If you didn't have to pay that excess cost you could have paid the plumber yourself.

The only service he's providing here is scheduling an appointment with a plumber who is the one actually fixing the pipes, not the landlord.

He's also trying to make a profit so the rent minus cost of mortgage and minus cost of repairs that he covers is almost still a positive number so that he is actually making money on this.

Again I want to stress, the service he's providing is paying other people to do things for you with money that you gave him.