Konrad Most was considered a canine behaviour expert in his time. It doesn't mean his methods were right, just that, based on the knowledge available at the time he was highly experienced. Things change, scientific knowledge and our understanding of other species does indeed move on and develo as research takes place and we learn more.
No-one is accusing you of using cruel methods on your dogs. I have no idea how you train and am therefore not qualified to make that judgement. For my part, I am just concerned that the OP, whose dog has an issue with aggression of some sort, is being directed to a behaviourist who describes pack theory and mentions dominance on their website:
"The language of the dog has evolved from wolf pack behaviour. Understanding the pack hierarchy will assist you to encourage positive behaviour between dogs and humans in the home.
The basis of this technique is understanding and utilising the language of the dog as a pack animal, enabling us to communicate with our dogs through body language."
The idea that domesticated dog behaviour is based on wolf pack behaviour has been scientifically disproven. Domestic dogs do not live or act as packs, nor do they consider humans part of their packs or create the kind of hierarchical pack structure believed (once - as this too is now in question) to exist in wolf packs. Therefore utilising methods based on pack theory and dominance hierarchy is an absolute nonsense.
I have to say the phrase "Through pressure and release you demonstrate to the dog that you are the 'Alpha' or 'Leader' and to be trusted and followed." is something that worries me - a lot. That sounds awfully like traditional punitive dog training, which however you look at it is cruel, usually, both physically and psychologically.
There's a world of difference between being dogmatic and choosing to follow only, sound scientific research that proves that we do not need to force dogs to submit to us in order to live peacefully with them in our society.