I don't know that I've ever owned an aggressive dog - I've certainly owned assertive dogs. Not a one of them has been mean. I do think there is a danger in telling people they need to be the alpha dog that they think that means they can bully the dog and so in that sense what you're saying may be true. But a good leader doesn't need to be a bully. My dogs have submitted to me over the years because they have loved and respected me.
You are correct—a good leader is what dogs need (clear communication of expectations, structure, consistency, etc.)
Leadership is what fosters the kind of relationship you have with your dogs. My view is that your dogs are following a good leader who is a very effective communicator, rather than submitting to your dominance.
You are also correct in that a breed’s temperament is definitely a factor in every aspect of training, so tone of voice, animation, choice of rewards, all need to be tailored to the temperament of individual dogs.
There are also definitely “normal” vs. “abnormal” behaviors in dogs and special care must be taken in working with abnormal dogs. There is usually a physiological basis (genetics, malnutrition, neurological damage at birth) for obsessive-compulsive, anxiety and other disorders seen in dogs, but the behavior can be exacerbated by poor early socialization and/or inappropriate training methods.
If you read more on dominance research, you will find that dogs are constantly switching roles in their packs, so even among dogs, dominance theory as commonly discussed among dog trainers does not hold.